From CNN NAJAF, Iraq (CNN) -- U.S. Marines battling militants in Najaf conducted a raid on Muqtada al-Sadr's house Thursday, but the renegade cleric was not there, CNN has learned. Authorities believe he could be holed up in the Imam Ali Shrine compound with other militia fighters. The compound is surrounded by Iraqi forces, but there is no plan to storm the site. Great caution and care is being taken not to disturb that site, one of the holiest in Islam. U.S. Marines and soldiers said they have control of the center of the city. There was an earlier report that Marines conducted an operation at a site near al-Sadr's house. Also, when an Iraqi official was asked about a raid on al-Sadr's house, he said that it is not known where the cleric resides. The news of the raid came after Iraqi officials, at a press conference, said fighters have been firing mortars from the sacred site and have laid land mines there. The military assault by U.S. and Iraqi forces includes tanks, heavy weapons and armored vehicles, with helicopter gunships patrolling overhead. Thick black smoke could be seen rising from the city for miles. "The Mehdi militia forces have been confined to a fairly small portion in the center of the city of Najaf," said U.S. Marine Lt. Col. Thomas Johnson.. "They have attacked Iraqi police stations near there, but the Iraqi police have decisively repelled each attack." Interim Iraq Prime Minister Ayad Allawi on Thursday called on militants loyal al-Sadr to lay down their weapons. Allawi's statement urged insurgents to "return to society." U.S. officials have accused al-Sadr, a maverick, anti-U.S. Shiite cleric, of fomenting unrest. He is wanted in connection with the killing of a rival cleric last year. Iraq's Health Ministry said Thursday that 25 militia members had been killed in Najaf in the 24-hour period ending at 9 a.m. Thursday. Another 153 were wounded. Up to 2,000 Marines in Najaf and about 1,800 soldiers from the Iraqi National Guard are in the area, U.S. military officials said. The U.S. Army's 1st Cavalry Division is also there. In a statement, al-Sadr was resolute about continuing the battle but thanked those people who worked to establish peace in the city. Al-Sadr has promised a fight to the death against American forces. Heavy fighting in al-Kut Iraqi security forces Wednesday battled insurgents in al-Kut after they attacked city hall, police stations and National Guard barracks, the Coalition Press Information Center said. An Iraqi Health Ministry official said 75 Mehdi Army members were killed and another 148 were wounded in battles over the previous two days. In addition, 100 Mehdi Army militia members have been arrested, an Iraqi Interior Ministry spokesman said. According to the coalition information center, al-Kut's governor has contacted the anti-Iraqi forces in hopes of putting an end to the fighting. Al-Kut is about 100 miles (160 kms) southeast of Baghdad. Other developments # The fighting comes ahead of a three-day national conference starting this weekend in Baghdad, where delegates from across the country were to choose an advisory committee to work with the interim government. Despite the fighting, officials intend to go forward with the conference, a process that some in the government hoped al-Sadr would eventually embrace. # A British soldier was killed and another seriously wounded when an improvised explosive device detonated near a passing patrol in the southeast city of Basra, a British military spokesman told CNN. The incident took place midmorning Thursday. No further details were disclosed. # The U.N. Security Council unanimously approved a resolution Thursday to extend the U.N. mission in Iraq for a year, The Associated Press reported. Secretary-General Kofi Annan indicated the number of U.N. staff allowed in the country will be limited due to security concerns, the AP said. # Two U.S. Marines died late Wednesday when a CH-53 helicopter crashed in al Anbar province, west of Baghdad, the Coalition Press Information Center said. Three Marines were injured. With the deaths, 935 U.S. military personnel have died in Iraq since the start of Operation Iraqi Freedom. # At the same time the offensive began against the militia of radical Shiite cleric Muqtada al-Sadr, thousands of his supporters Thursday rallied in Baghdad's Kadhmiya neighborhood -- a Shiia stronghold -- waving banners and calling for an end to violence and bloodshed. Some banners criticized President Bush and interim Iraqi PM Ayad Allawi while others pledged support for al-Sadr. # Controversial politician Ahmed Chalabi is in Iraq to face an arrest warrant, a spokesman for his Iraqi National Congress group said Wednesday. Chalabi is "in very high spirits and ready to face anything," the spokesman said. The warrant charges the former exile leader with counterfeiting. Also Wednesday, Chalabi's daughter Tamara announced in Washington that her father has filed a lawsuit against the government of Jordan. (Full story) CNN's Matthew Chance in Najaf, and Roaa Ahmed, Kevin Flower and John Vause contributed to this report. Copyright 2004 CNN. All rights reserved.This material may not be published, broadcast, rewritten, or redistributed. Associated Press contributed to this report.