At least 17 people have been killed by a car bomb in the holy city of Najaf - among them leading Shia Muslim politician Ayatollah Mohammed Baqr al-Hakim.
Mohammed Baqr al-Hakim had returned from exile this year
The bomb blew up near the Tomb of Ali in the central Iraqi city, one of the holiest shrines for Shia Muslims, just as main weekly prayers were ending.
No group has admitted carrying out the attack.
But correspondents say that a power struggle has been going on within what is known as the Hawza - the Shia religious establishment based in Najaf.
Ayatollah Mohammed Baqr al-Hakim was leaving the shrine after saying Friday prayers when the bomb went off.
The leader of an Iran-backed group, the Supreme Council for the Islamic Revolution in Iraq (Sciri), Ayatollah al-Hakim had returned to Iraq in May, after spending more than two decades in exile in Iran.
Eyewitnesses described a scene of bodies scattered on the ground as the injured wandered around the square in panic.
An Iraqi boy shouts a slogan denouncing U.S. troops occupying the country in the Shi'ite Muslim neighborhood of Sadr City before Muslim Friday prayers in Baghdad August 29, 2003. Iraqi Shi'ite Muslim leader Mohammed Baqer al-Hakim was killed by a car bomb in the Iraqi city of Najaf on Friday, his nephew Mohsen Hakim, a top official for the Supreme Council for the Islamic Revolution in Iraq (SCIRI) based in Tehran, told Reuters. REUTERS/Aladin Abdel Naby
The BBC's Valerie Jones, in Baghdad, said part of the entrance to the mosque is said to have collapsed on the crowd, and many people are feared to be trapped by the debris.
A restaurant was also badly damaged in the blast.
A US military spokesman said no coalition forces were in the area "because it is considered to be sacred ground".
On Sunday, three people were killed there in an assassination attempt on another leading Shia Muslim cleric.
Grand Ayatollah Seyed Mohammed Said al-Hakim received only scratches in the blast at his office but two of his bodyguards and a driver were killed.
Grand Ayatollah Seyed Mohammed Said al-Hakim is the uncle of the Sciri leader.
Other Iraqi Shia blamed the attack on agents of the former regime of Saddam Hussein.
And others are critical of the Americans, whom they hold responsible for the country's continuing insecurity.
Najaf was the scene of the brutal killing four months ago of Abdel-Majid al-Khoei, a prominent cleric who had returned from exile in London.
Copyright 2003 BBC