Baghdad, Iraq ? U.S. warplanes blasted insurgent positions in Sadr City, and American ground troops pushed into the sprawling Baghdad slum Thursday in a new operation aimed at disarming the militia of a renegade anti-U.S. Shiite cleric.

Despite violence sweeping the country, Iraq’s top Shiite Muslim cleric Grand Ayatollah Ali al-Sistani is insisting elections promised for January must be held on time, an aide said.

With car bombs, shootings and kidnappings escalating and several cities effectively under insurgent control, there are concerns that Iraq will not be ready to have a vote by the Jan. 31 deadline. But Shiites, who make up about 60 percent of Iraq’s 25 million people, are eager to have elections since they expect to dominate whatever government emerges.

Interim Prime Minister Ayad Allawi, in a speech to a joint session of the U.S. Congress on Thursday, vowed to not let violence derail the election timetable. He said 14 or 15 of Iraq’s 18 provinces “are completely safe.”

However, at least six provinces — Baghdad, Anbar, Diyala, Salahuddin, Kirkuk and Nineveh — have been the scene of significant attacks on U.S. troops and Iraqi authorities in the past month. The only areas not plagued by bloodshed are the three northern provinces controlled by Kurds. The situation in many areas, however, is unknown because journalists’ travel is restricted by security fears.

Allawi also condemned the beheading of two Americans, and relatives of a British hostage pleaded for his freedom. The appeal came after U.S. and Iraqi authorities refused militants’ demands to release female Iraqi prisoners.

American warplanes and helicopters were again in action Thursday over Sadr City, after a day of fierce clashes between U.S. troops and fighters loyal to rebel cleric Muqtada al-Sadr. Iraqi doctors said one person was killed Thursday and 12 were wounded, many of them children.

Militia fighters returned fire with machine guns and an American fighting vehicle was hit by a rocket-propelled grenade and caught fire, according to a U.S. report. It was not clear if there were casualties.

The aim of the Sadr City operation, dubbed “Iron Fist 2,” is to subdue al-Sadr’s Mahdi Army militia by seizing weapons caches and detaining or killing his lieutenants, said Maj. Bill Williams of the 1st Cavalry Division.

“The main problem is that he has the militia,” he said. “Our goal is to pressure him to disband and disarm.”

U.S. commanders have said the Mahdi Army has dug into the alleyways of Sadr City, a district named after al-Sadr’s late father.