Baghdad, Iraq ? Iraq’s interim prime minister on Sunday warned that efforts to resolve the standoff in Fallujah peacefully had entered their “final phase” and said he would not hesitate to launch “a military solution” to end Sunni insurgents’ hold over the city.

In another city of Iraq’s stormy Sunni Triangle, a rocket slammed into the Sunubar Hotel in Tikrit late Sunday, killing 15 Iraqis and wounding eight others, hospital officials said. Insurgents may have been aiming at an American position, which was targeted by a second rocket. U.S. officials said no American casualties were reported.

Prime Minister Ayad Allawi’s warning, delivered in a nationally televised news conference, occurred as U.S. forces prepare for a showdown with thousands of militants holed up in Fallujah, the city that has become the focal point of armed resistance to the Americans and their Iraqi allies.

Allawi appeared to be aiming to prepare the Iraqi public for an onslaught likely to unleash strong passions, especially among the country’s Sunni Muslim minority.

He warned of civilian casualties, saying that if he ordered an assault it would be with a “heavy heart,” because “there will be some loss of innocent lives.”

“But I owe, owe it to the Iraqi people to defend them from the violence and the terrorists and insurgents,” he said.

U.S. and Iraqi commanders want to put down guerrillas before vital elections planned for Jan. 31, which Allawi insisted will take place as scheduled. On Sunday, insurgents in Fallujah fired mortar rounds and rockets at U.S. Marines, who responded with artillery. U.S. aircraft also struck suspected rebel positions, Marine officials said.

Clashes were also reported between U.S. forces and insurgents in Ramadi, west of Fallujah, killing seven Iraqis and injuring 11, hospital officials said.

As night fell in the Iraqi capital, the rumble of powerful explosions could be heard coming from the western edge of the city but the cause of the blasts could not be determined.

The blast in Tikrit, 80 miles north of Baghdad, sent frightened guests of the three-story hotel running into the street.

U.S. military officials blamed the attack on “anti-Iraqi forces,” the term they use for insurgents. They said two rockets were fired, one of which exploded near an American military position but caused no damage or casualties.

U.S. officials say Allawi would personally issue the final order to launch any all-out assault on Fallujah.

U.S. Marine Staff Sgt. Timothy LaSage, of Milwaukee, a sniper with the 2nd Battalion, 5th Marine Regiment, scans the horizon during a gun battle with insurgents in Ramadi, Iraq. One Marine was killed and three others injured by a roadside bomb Sunday in Ramadi.