NEAR FALLUJAH, Iraq (AP) – U.S. warplanes pounded Fallujah late Friday in what residents called the strongest attacks in weeks as more than 10,000 American soldiers and Marines massed for an expected assault. Iraq’s prime minister warned the “window is closing” to avert an offensive.

Residents reached by telephone said the aircraft were striking targets in the central city market that had not been hit since April. There was no confirmation from U.S. officials.

Earlier Friday, U.S. planes dropped leaflets urging women and children to leave the city, residents said.

As pressure mounted on the guerrilla stronghold, the insurgents struck back, killing one U.S. soldier and wounding five in a rocket attack. Clashes were reported at other checkpoints around the city and in the east and north of Fallujah late in the day.

For the past three nights, long convoys of American soldiers from Baghdad and Baqouba have rolled onto a dust-blown base on the outskirts of Fallujah, a city that has become the symbol of Iraqi resistance. U.S. commanders here have been coordinating plans either to fight their way into the city or isolate it from the rest of Iraq’s Sunni Muslim heartland.

If they fight, American troops will face an estimated 3,000 insurgents dug in behind defenses and booby traps. Military planners believe there are about 1,200 hardcore insurgents in Fallujah – at least half of them Iraqis. They are bolstered by insurgent cells with up to 2,000 fighters in the surrounding towns and countryside.

In Brussels, Belgium, Iraq’s interim prime minister, Ayad Allawi, warned that the “window is closing” to avert an assault on Fallujah, 40 miles west of the capital. Allawi must give the final go-ahead for the offensive, part of a campaign to curb the insurgency ahead of national elections planned for January.

Sunni clerics have threatened to boycott the election if Fallujah is attacked, and U.N. Secretary-General Kofi Annan has warned U.S., British and Iraqi authorities that a military campaign and “increased insurgent violence” could put elections at risk.

U.S. aircraft struck targets around Fallujah in numerous raids starting late Thursday and continuing into Friday night. Targets included a system of barriers rigged with bombs, a command post, suspected fighting positions and a weapons cache, according to Lt. Nathan Braden of the 1st Marine Division.

Late Friday, U.S. jets went into action again, striking several targets in the Jolan sector of northern Fallujah, residents said. Jolan is considered one of the most heavily defended neighborhoods in the city. As the night dragged on, the attack was expanded to targets in the center of the city, according to residents. Artillery fire could also be heard. The drone of U.S. aircraft heading toward Fallujah could be heard over the Iraqi capital Baghdad.

Mortar shells exploded on a small U.S. base at Saqlawiyah west of Fallujah, the military said. U.S. troops returned fire, killing a number of insurgents, the military said.

Iraqi authorities closed a border crossing point with Syria, and U.S. troops set up checkpoints along major routes into the city. Marines fired on a civilian vehicle that did not stop at a checkpoint in Fallujah, killing an Iraqi woman and wounding her husband, according to the U.S. military and witnesses. The car didn’t notice the checkpoint, witnesses said.

“Marines fire upon vehicles only as a last resort when verbal and visual warnings to stop fail. Such was the case today,” the Marines said in a statement.

The violence came a day after two Marines were killed and four were wounded in fighting west of Baghdad. The Marine command gave no further details, citing security.

A U.S. soldier was killed and another wounded when a roadside bomb hit their vehicle north of Baghdad on Thursday.

Elsewhere, U.S. Cobra attack helicopters fired Friday on insurgents operating an illegal checkpoint south of Baghdad, killing or wounding an “unknown number” of people, the military said.

Allawi has demanded that Fallujah hand over foreign extremists, including Jordanian terror mastermind Abu Musab al-Zarqawi and his followers, and allow government troops to enter the city.

“We intend to liberate the people and to bring the rule of law to Fallujah,” Allawi said in Brussels after meeting with European Union leaders. “The window really is closing for a peaceful settlement.”

Zarqawi’s followers claimed responsibility for the suicide attack that killed three British soldiers south of Baghdad on Thursday, according to a statement posted on an Islamist Web site. The claim could not be verified but appeared on a Web site often used by militants to post claims.

Allawi, a secular Shiite Muslim with strong ties to the CIA and State Department, urged the Europeans to forge a “close and strategic partnership” with Iraq and called on NATO to step up plans to train 1,000 officers a year for the Iraqi military.

EU leaders responded with a nearly $40 million offer to fund elections, including training for Iraqi vote monitors.

French President Jacques Chirac – who opposed the Iraq war – skipped a meeting with Allawi to fly to Abu Dhabi to pay his respects to the new president of the United Arab Emirates, who took over after the death of his father. Many saw it as a snub of Allawi, although Chirac denied that, describing his relations with the new Iraqi authorities as “excellent.”

Allawi faces strong opposition to a Fallujah offensive from the Sunni minority. The Sunni clerical Association of Muslim Scholars has threatened to boycott the January election and mount a nationwide civil disobedience campaign.

A public outcry over civilian casualties prompted the Bush administration to call off the siege of Fallujah in April, after which the city fell under control of radical clerics and their followers.

Those warnings were echoed by Annan in a letter dated Oct. 31 to American, British and Iraqi leaders. A copy was obtained by The Associated Press.

“I have in mind not only the risk of increased insurgent violence, but also reports of major military offensives being planned by the multinational force in key localities such as Fallujah,” Annan wrote.

Nevertheless, U.S. and Iraqi authorities appear committed to a showdown with the city of an estimated 300,000 residents.

In hopes of assuaging public outrage, Iraqi authorities have put together a team of administrators to run Fallujah after the offensive and have earmarked $75 million to repair the damage, Marine Maj. Jim West said.

The strategy is similar to one used when U.S. troops restored government authority in the Shiite holy city Najaf last August after weeks of fighting with militiamen.

AP-ES-11-05-04 1717EST