Over the past decades, Saudi Arabia was targeted by different terror groups: Iran affiliated Shia terror groups, Al Qaeda and the Islamic State (IS). In response, it developed a comprehensive and effective approach to fostering security by countering and deterring terrorism.
The Zulfi incident (April 2019)
On April 21, 2019, four heavily armed terrorists were killed on April 21, 2019, in a failed attack on an interior ministry building in Zulfi, a small city northwest of the capital Riyadh.
The Islamic State linked Amaq news agency released a video on April 22, 2019, of the four alleged “martyrdom-seekers” behind the attack. In the video, one man says the attack is to avenge Muslims imprisoned in the Kingdom, Syria, and Iraq. It’s unclear when the footage was filmed.
The attack 
The attackers were armed with machine guns, bombs, Molotov cocktails and "suicide belts".
The suspects who were on board a car tried to crash through the main entrance of the General Directorate of Investigation’s Center in Zulfi, but were intercepted by security and prevented the vehicle from gaining access into the compound.
Two gunmen died after opening fire on police, who killed them, one was killed as he attempted to flee, while the fourth attacker died as he tried to blow up an explosive belt.
The Saudi security forces found 5 explosive belts, four of which were worn by the perpetrators, and another inside a car. The belts contained detonating keys and grenades with shrapnel-like screws.
The investigation of the Islamic state's terror network
Saudi authorities discovered a house in Al-Rayyan neighborhood in Zulfi governorate, rented by one of the four terrorists, where they found what resembled to be a factory for manufacturing explosives and explosive belts. Authorities seized 64 homemade grenades, 61 pipe fittings, of which nine were being processed as pipe bombs, three mobile phones, and three pressure cookers ready for detonation, two Kalashnikov machine guns, six pistols, and other various weapons. They also found four bags containing organic fertilizers, along with sets of laboratory glass containers, a number of plastic containers, a package of liquid chemical containers, sulfur-fiber cartons, a homemade explosive detonator and a set of screws that were equipped with shrapnel. Authorities also seized a set of ATM cards, two national identity cards, SR 228, a number of publications and CD-ROMs with content related to terrorist organization. Thirteen people were arrested after finding plans to execute criminal acts that were targeting the Kingdom’s security, probably connected to the Islamic state network. 
The terror threats in Saudi Arabia
The Houthi threat – since the Saudi intervention in the war in Yemen in 2015, Saudi Arabia received multiple cross-border ballistic missile attacks attributed to Houthi rebels in Yemen. The impacted area is diverse, including but not limited to a Red Sea coastal impact in Yanbu and Jasan, missiles launched against the capital, Riyadh, and strikes in the Yemen-Saudi border region, to include Khamis Mushayt. The Houthi rebels also launched attacks by armed drones across the border.
The internal terror threats - different armed groups have targeted security and government installations in the last two years in Saudi Arabia. Some of the terror groups were Islamic state affiliates and the rest belonged to Shia resistance groups.
Saudi Arabia's Shia community - accounts for between 10 to 15 percent of the total population. Saudi Arabia's Shia population is mostly based in two oasis districts of the Eastern Province, Qatif on the Gulf coast, and al-Ahsa, southwest of the provincial capital al-Khobar. Qatif and Al-Ahsa have historically been the focal point of anti-government demonstrations since February 2011. Protesters have been demanding reforms, freedom of expression and the release of political prisoners. They want an end to economic and religious discrimination against the oil-rich region.
Shias say they face discrimination in seeking educational opportunities or government employment and that they are referred to disparagingly in text books and by some Sunni officials and state-funded clerics. They also complain of restrictions on setting up places of worship and marking Shia holidays, and say that Qatif and al-Ahsa receive less state funding than Sunni communities of equivalent size.  The Saudi government denies allegations of discrimination.
Over the past years, Saudi forces have cracked down on anti-government protesters in Awamiya and other towns in Qatif and more than 20 anti-government protesters have been killed by the security forces since 2011.
Sheikh Nimr al-Nimr, a prominent opposition Shia cleric, with a popular power base in the region, was sentenced in 2014 to death and was executed in January 2016. In response to the execution of Nimr, several thousand demonstrators stormed the Saudi embassy in Tehran and following the attack, Saudi Arabia announced that it break off diplomatic relations with Iran.
The threat of ISIS and Al Qaeda
ISIS leader Abubaker Al Baghdadi released a recording on August 22, 2018, titled "Give Glad Tidings to the Patient," in which he urged his followers all over the world to wage terrorist attacks, and to reassure his “followers” over the group’s recent losses in Syria and Iraq. The recording was released on Al Furqan, the ISIS media center. 
Al Baghdadi has been consistent in his attacks and incitement against the Kingdom of Saudi Arabia and the reforms the Saudi government is pursuing. In his speech, Al Baghdadi also attacked Saudi Arabia by saying that the Kingdom “Is trying to secularize its inhabitants and ultimately destroy Islam.” He then urged the citizens of Saudi Arabia to overthrow their government, adding that “America is going through the worst time in its entire existence”.
In January 30, 2019, Islamic State has urged fanatical followers to bomb a Mariah Carey concert in Saudi Arabia. The group has been urged to stop the event which was seen to extremists as un-Islamic.
In May 2018, Al Qaeda published a bulletin that described religious reforms in the Kingdom of Saudi Arabia as “heretical and urged clerics to rise against moderate, open Islam, which all onlookers know is American Islam.”
Examples of internal terror incidents:
The Abu Hadriyah incident - two suspects armed were killed and two others arrested on April 9, 2019, after they attacked a security checkpoint in Qatif governorate, Eastern Province.
The attack occurred in Abu Hadriyah, in Qatif governorate, a highway linking the Eastern Province to Bahrain and Kuwait, as the assailants tried to flee the country.
In a preemptive operation in coordination with the Eastern Province security authorities, the Presidency personnel spotted four wanted terrorists in a SUV driving towards Abu Hadriyah Road.
When the security authorities blocked their way and ordered them to surrender, they started firing at the security men, so the latter fired back, leading to damaging the terrorists’ vehicle. They fled to a nearby gas station and threw a hand grenade, causing a fire in part of the gas station.
The al-Qouikeb incident - Saudi Arabia state security stated that three wanted terrorist were killed in Qatif province on September 27, 2018, after clashes with the security forces. Also, three security members were slightly injured.
The three terrorists were detected in a house located in the neighborhood of al-Qouikeb in the center of Qatif province.
The clashes erupted when the terrorists found that they are surrounded by the security forces, refusing to surrender and opening fire which prompted the security forces to retaliate.
The Al-Bukayriyah incident - on August 15, 2018, Saudi security forces attempted to arrest a suspected terrorist in the city of Al-Bukayriyah, Qasim province. In a subsequent exchange of fire, the assailant was shot and injured. No civilian or member of the security forces was killed or injured.
The Buraydah incident - a member of the security forces and a Bangladeshi resident were killed on July 8, 2018, in an assault on a security checkpoint in Buraydah in the Qassim province, north of the capital Riyadh. A security checkpoint on the Buraydah-Tarfiyah road in Qassim region came under fire from three terrorists riding in a vehicle. Two of the terrorists were killed and a third was wounded and arrested. ISIS claimed responsibility for an attack.
The Asir incident - four Saudi security personnel were killed and 4 others injured, on April 19, 2018, in a shooting incident in the Asir region (in the South-West of Saudi Arabia). The police caught 2 of the assailants, and killed the third.
The royal palace in Jeddah incident - two Saudi guards were shot dead and 3 others injured on October 7, 2017, when a man drove up to the gate of the royal palace in Jeddah and began shooting.
The operation in Riyadh - on October 5,2017, two suspected terrorists were killed during a security operation which took place across 3 sites in Riyadh.
The Grand Mosque in Makkah - on June23, 2017, Saudi security forces disrupted an imminent terrorist attack targeting the Grand Mosque in Makkah. During the security operation, which took place at one site in Jeddah and 2 sites in Makkah, a suicide bomber injured 11 people, including 5 members of the security forces.
The Saudi response to terrorism
The kingdom developed a comprehensive and effective approach to fostering security by countering and deterring Islamic radicalism and terrorism.
Intelligence sharing and operational coordination - they include cooperation and collaboration within the security sector and between security sector players and civil and other government instructions.
Counter terrorism training - Saudi security forces conducted on April 15, 2019, the "Al Watan 89" counter terrorism exercise in Al-Ahsa in the eastern region of the kingdom. The exercise followed similar training along the Kingdom’s northern borders and around Madinah.
The internal security forces participated in this exercise for several weeks, which was full of operational training in terms of command and control, as well as field tactical training by land, sea and air. Crack teams took part in car chases, hand-to-hand combat and vehicle assault demonstrations, and used helicopters and explosives to show the Kingdom’s level of readiness for dealing with any serious internal security threats.
Preventive measures - constraints on making, importing, selling, possessing, dealing, or acquiring weapons, munitions, and chemical materials.
Terrorism financing and money laundering - in 2002 the kingdom established a unit for financial investigations and a standing national counterterrorism committee.
The kingdom is working with the international “Financial Action Task Force on Money Laundering,” and also participated in counterterrorism-related working groups at the “G20 summit” and implemented the recommendations that arose from them.
Countering Islamic radicalization - in 2017, Saudi Arabia established in Riyadh the “Global Center for Combating Extremist Ideology” (Etidal) as well as the “Center for Cultural War,” a new division of the Saudi Ministry of Defense.
The legal measures – Saudi Arabia is dealing firmly with perpetrators of terrorist crimes and they are pursued vigorously and prosecuted according to the legal and statutory measures. These measures are in accord with Islamic legal principles.
Saudi Arabia announced on April 23, 2019, that it had executed 37 citizens who had been convicted of "terrorism", with one of the bodies of the condemned crucified after death. The sentences were carried out in Riyadh, the holy Muslim cities of Mecca and Medina, Qassim province, as well as Eastern Province which is home of the kingdom's Shia minority. It said that one person was crucified after his execution, a punishment reserved for particularly serious crimes. 
Saudi government capacity to combat transnational and domestic terrorism has increased over the past several years and the government security forces have increased their capacity to respond quickly anywhere in the Kingdom.
Saudi Arabia has carried out a number of counterterrorism operations and has arrested and disrupted active terrorist cells throughout the kingdom.
Saudi Arabia has implemented counter terrorism legislation and upgraded law enforcement and border security systems and has expanded existing counterterrorism programs and projects to rehabilitate terrorist fighters.
Saudi Arabia is also a member of the Financial Action Task Force for the Middle East and North Africa, a regional body that imposes financial sanctions on individuals and groups that help to fund terrorism. Saudi Arabia has maintained strict control over the banking sector and tightened sanctions on the financing of terrorism.
The kingdom establishes in 2015 the “Islamic Military Counterterrorism Coalition,” bringing together 41 Islamic countries. Meanwhile, under the auspices of the UN, the kingdom ratified and joined all of the organization’s 16 counterterrorism agreements.The Kingdom of Saudi Arabia is committed to uprooting all forms of extremism and terrorism and will remain a crucial partner in the war against terrorism.
 Four killed in failed terrorist attack on interior ministry building north of Riyadh, Arab News, April 21, 2019.
 IS claims attack in Saudi Arabia, Al Arabiya, April 22, 2019.
 Four killed in failed terrorist attack on interior ministry building north of Riyadh.
 Saudi Arabia arrests 13 accused of planning terrorist attacks, Arab News, April 2, 2019.
 Saudi Arabia: The al-Zulfi attackers are IS members, Al Arabiya, April 22, 2019.
 Saudi Arabia arrests 13 accused of planning terrorist attacks.
 This paper is not analyzing the external threats from Yemen and the Saudi response.
 At least 21 killed in ISIL bombing in Saudi Arabia’s Qatif, Press TV, May 22, 2015.
 Five killed in Saudi Arabia shooting, Al Jazeera, November 4, 2014.
 Saudi police officer killed in Eastern Province , Press TV, April 6, 2015.
 IS Leader Threatens Saudi Arabia In Latest Speech, The Embassy of the kingdom of Saudi Arabia in Washington D.C, August 29, 2018.
 IS call for terror attack on Mariah Carey concert in Saudi Arabia tomorrow night, Daily Mail, January 30, 2019.
 IS Leader Threatens Saudi Arabia in Latest Speech, The Embassy of the kingdom of Saudi Arabia in Washington D.C, August 29, 2018.
 Saudi State Security: Three wanted in terror related activities killed in Qatif, Al Arabiya, September 27, 2018.
 Two killed in attack on security checkpoint in Saudi Arabia's Qassim: Interior ministry, Press TV, July 8, 2018.
 Watan 89’: Saudi security forces’ explosive display of firepower, Arab News, April 15, 2019.
 Saudi Arabia executes 37 citizens for 'terrorism', the new Arab, April 24, 2019.
 Saudi Arabia participates in forum against terrorism, Arab News, October 20, 2018.