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 neighbouring 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.

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