US and Iraqi forces killed 250 gunmen in a fierce battle involving US tanks and helicopters on the outskirts of the Shia holy city of Najaf today, a senior Iraqi police officer has said.
A US helicopter was shot down in the fighting, Iraq security sources said. The US military has declined to comment.
Shia political sources said the gunmen appeared to be both Sunni Arabs and Shias loyal to a cleric called Ahmed Hassani.
Meanwhile, in Baghdad, 13 people were killed in bombings in mainly Shia areas, police said.
Twin car bombs targeting ethnic Kurds killed 16 people as night fell in the northern oil city of Kirkuk, whose population is a volatile mix of Kurds, Turkmen and Sunni and Shia Arabs.
Hundreds of thousands of pilgrims have converged on Iraq's other main Shia holy city, Kerbala, for Ashura, marking the 7th century Battle of Kerbala, which helped consolidate the schism between Shia and Sunni Islam. It ends on tomorrow.
It is the first time the 10-day annual ritual has been held since violence erupted last February between Iraq's majority Shia and once-dominant minority Sunnis.
The governor of Najaf province said Iraqi troops fought a day-long battle with up to 200 Sunni gunmen, including foreign fighters, in orchards on the northern outskirts of the city, seat of Iraq's most powerful Shia clerics.
Governor Asaad Abu Gilel said the authorities had uncovered a plot to kill some of the clerics on Monday, to coincide with the climax of Ashura.
"There is a conspiracy to kill the clergy on the 10th day of Muharram," Najaf governor Abu Gilel said, referring to the day of the Muslim calendar on Monday.
A Reuters reporter about 1.5 km from the fighting said he heard intense gunfire and saw US helicopters rocket groves sheltering militants. He saw smoke trailing from one helicopter before it came down in the midst of the fighting.
He was unable to see what had happened to the helicopter, but officers in Iraq's 8th Army Division and policemen said it had crashed and that the two crew members were dead. The US military said it did not comment on operations still taking place.