RIYADH, Saudi Arabia — A suicide bomber blew himself up in the parking lot of a Shiite mosque in eastern Saudi Arabia during Friday prayers, killing four people in the second such attack in as many weeks claimed by the Islamic State group.
The attack, which set vehicles alight and sent a cloud of black smoke into the air, came after a suicide bombing a week ago at another Shiite mosque killed 21 people, heightening sectarian tensions in the Sunni-majority kingdom.
Both attacks took place in the oil-rich east, which has a sizable Shiite majority that has long complained of discrimination. The Islamic State group and other Sunni extremists view Shiites as apostates deserving of death.
There were conflicting reports of the attack, which took place after worshippers packed the Imam Hussein mosque, the only Shiite mosque in the port city of Dammam.
The state-run Saudi Press Agency said security guards halted a car in the parking lot of the mosque and that the bomber detonated his payload as they approached. "Thank God, security authorities managed to foil a terrorist crime targeting worshippers," the agency said in a statement. It was unclear if the bomber was among the four dead.
A security official told The Associated Press that the attacker had disguised himself in the black all-encompassing garments worn by women in Saudi and blew himself up after being stopped by security guards. He insisted on anonymity because he was not authorized to speak to the media.
Mohammed Idris, an eyewitness, told the AP by telephone that the suicide bomber attempted to enter the mosque but was chased by young men, who had set up checkpoints at the entrance of the mosque.
"They chased the suicide bomber when he tried to enter the women's section of the mosque in the south entrance," he said. He identified one of the dead as Abdul-Jalil Abrash, a 25-year-old graduate student from an American university.
Ali Jaafar, another eyewitness, told the AP that the explosion set several cars on fire.
"It was big and loud," he said. "The whole thing was very disturbing."
A third witness, who did not want to be named because of security concerns, said he saw the remains of a victim in the parking lot. He said that security had been tightened at mosques because of last week's attack and that women were told not to come because of a lack of female searchers to check them.
Mohammed al-Saeedi, who arrived half an hour after the blast, said by phone that four cars were damaged by the explosion, and body parts apparently from the bomber were scattered around the site.
"Pieces of the body were everywhere at the main gate and in the roof of the mosque," he said. He called on police to do a better job of sharing information with the local Shiite community to protect against future attacks.
The Islamic State group claimed responsibility for the attack, saying it was carried out by its "Najd Province," referring to a region in the central Arabian Peninsula.
A statement posted on a Facebook page used by the extremist group said a "soldier of the caliphate," identified as Abu Jandal al-Jazrawi, blew himself up among "an evil gathering of those filth in front of one of their shrines in Dammam." The name al-Jazrawi suggests that the bomber is a Saudi national.
It called on Sunnis to "purify the land of the two shrines from the atheist rafida," a derogatory term for Shiites.
Last Friday, an Islamic State suicide bomber killed 21 people in the village of al-Qudeeh, in the oil-rich eastern Qatif region. It was the deadliest militant assault in the kingdom since a 2004 al-Qaida attack on foreign worker compounds. Saudi Arabia's king vowed to punish those responsible for last Friday's "heinous terrorist attack."
Saudi Arabia's Shiite minority is a branch of Islam that both the Islamic State group and ultraconservatives in Saudi Arabia regularly denounce as heretical. Shiites in Saudi Arabia have long complained of discrimination and say their communities have benefited little form the country's vast oil riches, which are also concentrated in the east.
In 2011, Shiites in the east inspired by the Arab Spring uprising in neighboring Bahrain took to the streets to demand greater rights. Police arrested hundreds of people and a counterterrorism court sentenced an outspoken cleric, Nimr al-Nimr, to death.
Saudi Arabia views Shiite movements elsewhere in the Middle East as proxies of its main regional rival, Shiite-majority Iran. Riyadh is currently leading a coalition in bombing raids against Shiite rebels in neighboring Yemen, known as Houthis, who seized the capital, Sanaa, last year.
Associated Press writers Maggie Michael in Cairo, Reem Khalifa in Manama, Bahrain, and Adam Schreck in Dubai, United Arab Emirates, contributed to this report.