An Islamist militant suicide bomber disguised as a woman blew himself up outside a Shi'ite mosque in eastern Saudi Arabia on Friday, killing himself and three other people, the second attack of its kind in the world's top oil exporter in one week.
The bombing, which was claimed by Islamic State, could further escalate sectarian strife in the kingdom, where anti-Shi'ite sentiment has been stoked by a military campaign against Iranian-allied Houthi militias in neighboring Yemen since March.
The Interior Ministry said a suicide bomber disguised in women's clothes blew himself up outside the al-Anoud mosque's entrance in the city of Dammam during noon prayers.
Witnesses said a suicide bomber, who wore an Abaya used by women in Saudi Arabia, blew himself up in the mosque's parking lot when guards searching worshippers became suspicious of him.
The ministry said four people, including the bomber, were killed in the blast, which also set several cars ablaze.
Residents circulated pictures of the body of a man believed to be the suicide bomber as well as pictures of black clouds of smoke billowing over a parking lot outside the mosque.
Video posted on social media showed the congregation inside the mosque reacting with shock and alarm to the noise of the explosion outside the building.
An Islamic State statement named the suicide bomber as Abu Jandal al-Jizrawi and said he had managed to reach his target despite heightened security.
Islamic State claimed responsibility for a suicide bombing last week at a Shi'ite mosque in al-Qadeeh village, near al-Qatif city, that killed 21 and wounded nearly 100 in the bloodiest militant attack in the kingdom in years.
Saudi Arabia, which is leading an Arab coalition in a campaign against the Houthis who have seized power from Yemeni President Abd-Rabbu Mansour Hadi, had sought to calm sectarian tensions.
Saudi Arabia's King Salman has denounced the al-Qadeeh bombing and promised to punish anyone linked to it. King Salman also sent Crown Prince Mohammed bin Nayef to convey condolences to the families.
Members of Saudi's Shi'ite minority staged separate protest in Dammam and in the village of al-Qadeeh on Friday evening, demanding an end to sectarianism, witnesses said.
Islamic State openly acknowledges it is trying to stir sectarian confrontation as a way of hastening the overthrow of the ruling Al Saud family, and has urged young Saudi Sunnis in the kingdom to attack targets including Shiites.
Some commentators in Saudi Arabia discussing the Qadeeh bombing have said the kingdom has not done enough to crack down on online abuse of Shiites, a discourse which Shiites say provides an incubator for violence against the minority sect.
Sunni power Saudi and Shiite Iran are locked in a tussle for influence in the region, where wars have claimed hundreds of thousands of lives mainly in Syria, Iraq and Yemen.