FALLUJAH, Iraq — Multiple explosions shook Fallujah after dark Tuesday, and large plumes of smoke billowed into the sky as fighting erupted for the second straight night. An American AC-130 gunship hammered targets in the city.

Blasts and gunfire went on steadily for more than half an hour in sustained fighting, apparently in the northern Jolan district, a poor neighborhood where Sunni insurgents are concentrated.

Flames could be seen rising from building, and mosque loudspeakers in other parts of the city called for firefighters to mobilize.

The fighting erupted as a two-day extension to a cease-fire ended. Earlier in the day, U.S. aircraft dropped leaflets in the city of 200,000 people, calling on insurgents to surrender.

"Surrender, you are surrounded," the leaflets said. "If you are a terrorist, beware, because your last day was yesterday. In order to spare your life end your actions and surrender to coalition forces now. We are coming to arrest you."

Fighting in the same neighborhood on Monday night killed one Marine and eight insurgents, and tank fire destroyed a mosque minaret that U.S. commanders said insurgents were using as sniper's nest.

U.S. troops fought militiamen overnight near Najaf, killing 64 gunmen and destroying an anti-aircraft gun. An American soldier was killed Tuesday in Baghdad, raising the U.S. death toll for April to 115 — the same number lost during the entire invasion of Iraq last year.

The battle outside Najaf was one of the heaviest with the militia as U.S. troops try to increase the pressure on gunmen loyal to radical cleric Muqtada al-Sadr. U.S. troops moved into a base in Najaf that Spanish troops are abandoning, but promised to stay away from the sensitive Shiite shrines at the heart of the southern city.

On Sunday, the U.S. military had announced a two-day extension to the fragile cease-fire in Fallujah to give political efforts a chance — backing down from threats to launch an all-out assault on the city to root out insurgents. Brig. Gen. Mark Kimmitt had said there was no ultimatum for a launch of an assault if political efforts are not showing results.

"We don't think deadlines are helpful," Kimmitt said Tuesday.

Earlier Tuesday, Marines were pushing ahead with training for a key part of the political track, the introduction of U.S.-Iraqi patrols into Fallujah.

As the United Nations prepared to discuss the form of a caretaker government due to take power June 30, U.S.-appointed Iraqi leaders complained that the administration won't have real sovereignty as promised by American administrators for months.