Iraqi police say U.S. and Iraqi forces have killed 250 insurgents in a day-long battle on the outskirts of the Shi'ite holy city of Najaf.
Police sources in Najaf, south of Baghdad say the battle continued after darkness fell Sunday. The U.S. military has not commented.
Earlier on Sunday Iraqi officials said U.S. helicopters were backing up the operation. They said the insurgents were planning to assassinate Shi'ite clerics during the Ashura observances this week. Iraqi and U.S. officials also said a U.S. helicopter crashed during the battle. U.S. authorities say two American soldiers were killed.
In other news, Iraqi officials said on Sunday that attacks in Baghdad killed at least 15 people, and car bombs in Kirkuk, in northern Iraq, killed another 16.
In one of the deadliest attacks in the capital, mortar shells landed on a school in a Sunni district of the capital, killing at least four girls.
The U.S. military announced that three more American troops were killed in Iraq.
Thousands of Iraqi soldiers and police are deploying around the city of Karbala to provide security for Shi'ite pilgrims during the solemn observances of Ashura.
Ashura marks the seventh century slaying of the Shi'ite Imam Hussein, grandson of the Prophet Muhammad, at Karbala. Shi'ites believe Hussein was the prophet's heir. Hussein's death solidified Islam's split into rival Sunni and Shi'ite branches.
Karbala's governor, Akhil al-Khazali says Iraqi forces have begun blocking roads to prevent car bombs from reaching the city.