Muslim worshippers ran in panic after attackers set off bombs and fired shots in a mosque in Saudi Arabia.

Five died and 18 others were wounded. Attackers wore suicide belts and carried assault rifles into a Shi'ite mosque in eastern Saudi Arabia during Friday prayer services.

It was at least the fifth such attack in under a year.

Amateur video showed worshipers inside the Imam Reda Mosque as a bomb explodes. The explosion broke windows, doors and ceiling tiles. Men were heard shouting religious slogans. The lights went out and gunshots were heard.

Eyewitness Mohammed al Ahmed told Saudi TV that worshipers inside the mosque blocked its doors after the attack began. But one terrorist entered after the blast.

Several minutes after worshipers locked the doors, an explosion went off, he said. The lights went off and smoke filled the room. A man with an assault rifle took shots, but was wrestled to the ground and disarmed after he was hit with a chair.

Security forces exchanged fire with the attackers outside the building.

Al Arabiya TV reported that security forces arrested two men. Other media reported that one man was arrested and a second blew himself up.

At least four other such attacks on Shi'ite mosques have taken place inside Saudi Arabia during the past year. Saudi TV reported that security forces have been able to prevent more than a half dozen other attacks.

Middle East analyst Theodore Karasik told VOA that the attack Friday "is reminiscent of previous Islamic State attacks targeting Shi'ites." He said that IS has been calling for more attacks in recent weeks. This "may be the start of a new wave" in Saudi Arabia.

No group has yet claimed responsibility for the latest attack.