Fallujah, Iraq ? Insurgents and U.S.-allied Iraqi officials agreed in principle for a cease-fire in Fallujah starting today, but the deal depends on the doubtful prospect of American soldiers withdrawing from the city, a member of Iraq’s Governing Council said.

The comments late Saturday by Mahmoud Othman came as Marines, backed by hundreds of reinforcements, encircled the besieged city, which the U.S. military threatened to take by force if negotiations failed.

Early today, the Arab TV station Al-Arabiya reported that a Fallujah cease-fire would start at 6 a.m. A few hours later, the station Al-Jazeera quoted an unidentified insurgent leader as saying the deal would last 12 hours, and that forces would respect it.

But the American side had no immediate comment on any truce reached in talks between insurgents and Governing Council members that started Saturday, and Othman questioned the prospects for a deal given the demand by both sides.

“Fighters in the city say they want the Americans to withdraw, but I don’t know how likely that is,” he said.

Seeking to pressure the Americans further, insurgents who kidnapped a U.S. civilian Friday threatened to kill and mutilate him if Marines did not withdraw from Fallujah by 6 a.m. today local time, or 9 p.m. Saturday CDT. The deadline passed with no word on his fate.

Gunfire crackled in the city during the day Saturday, even as Iraqi government negotiators met with Fallujah leaders to persuade them to hand over militants who killed and mutilated four Americans here March 31.

Brig. Gen. Mark Kimmitt has called on Fallujah’s insurgents to join a bilateral cease-fire. But he said a third battalion of Marines had moved to the city, joining two battalions totaling 1,200 troops and a battalion of nearly 900 Iraqi security forces.

He said Marines were respecting a unilateral halt in offensive operations called Friday but said gunmen continued to fire on troops, who were responding.

“Were we not at this point observing suspension of offensive operations … it could well have been that we would have had the entire the city by this point,” Kimmitt said in Baghdad.

Asked what he hoped from the negotiations — in which U.S. officials were not taking part — Kimmitt said: “We would like to hear that they will lay down their arms … (and) are prepared to turn over the perpetrators of the attacks on the Americans.”

Militants threatened to kill U.S. hostage Thomas Hamill, 43, of Macon, Miss., whose capture Friday during another ambush in the area was the latest in a series of kidnappings.

“Our only demand is to remove the siege from the city of mosques,” a spokesman said in a videotape aired on Al-Jazeera. “If you don’t respond within 12 hours … he will be treated worse than those who were killed and burned in Fallujah” — referring to the Americans whose bodies were mutilated and two of them hanged from a Euphrates River bridge.