A suicide bomber has blown himself up in the parking lot of a Shiite mosque in an eastern Saudi city and killed four people, in the second deadly bombing targeting the religious minority in a week.

The Saudi Press Agency said the bomber was parking his car at the entrance of the Imam Hussein mosque in the port city of Dammam, home to a large Shiite population, during Friday prayers. It added that guards approached the car as it was parking and that the driver detonated a bomb.

"Thank God, security authorities managed to foil a terrorist crime targeting worshippers," the Kingdom's official news agency said. It was unclear if the bomber was among the four dead.

A security official said that the attacker had disguised himself in a black all-encompassing garment worn by women in Saudi and blew himself up after being stopped by security guards.

But eyewitnesses said that the attack was apparently foiled by a group of men who were suspicious of the bomber.

Religious authorities had asked women them to keep away from mosques during Friday prayers, as they are unable to carry out strict security checks on females and because they feared a repeat of a deadly attack one week ago against another Shiite mosque.

An attack last Friday killed 21 people in the village of al-Qudeeh, in the oil-rich eastern Qatif region.

Claimed by the Islamic State group, it was the deadliest assault by militants in the kingdom since a 2004 al Qaida attack on foreign worker compounds. 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.

Mohammed Idris, an eyewitness, said that the suicide bomber attempted to enter the mosque but was chased by young men, who had set up check points at the entrance of the mosque. He identified one of the dead as Abdul-Jalil Abrash, a 25-year-old graduate student from an American university.

"They chased the suicide bomber when he tried to enter the women's section of the mosque in the south entrance," he said.

Ali Jaafar, another eyewitness, said that the explosion set several cars on fire.

"It was big and loud," he said, adding, "the whole thing was very disturbing."

A third witness, who did not want to be named, said he saw the remains of the 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.