Iraqi insurgents fired a rocket-propelled grenade at the mayor's office in this restive city west of Baghdad (search-- the latest in a series of attacks against people thought to be cooperating with U.S. occupation forces.

Meanwhile, U.S. officials said that Syrian border guards detained during a firefight last week during an operation to hunt down suspected members of Iraq's ousted regime were still in U.S. custody.

U.S. troops shot and killed one of the ambushers on the mayor's office late Monday in Fallujah (search), a town 35 miles west of Baghdad, U.S. reports said. But local residents at the scene said the man killed was not involved in the attack and was caught in the crossfire.

Insurgents last week began targeting Iraqi civilians thought to be too close to Americans -- a new tactic in their campaign to disrupt the U.S.-led occupation.

A U.S. Army Military Police officer was slightly wounded late Monday in Khaldiyah (search), about 35 miles west of Baghdad, when insurgents fired a rocket-propelled grenade which struck a Humvee, said 1st Lt. Charles Mulcahey, a platoon leader with the 115th Military Police company.

An infantry platoon found no suspects or weapons after combing the thick palm scrub alongside highway 10, where the ambush took place.

Insurgents fired two more rocket-propelled grenades at U.S. troops in Habaniyah, about three miles west of Fallujah, but they exploded without causing injuries, reports said.

Details continued to emerge Tuesday on a previously undisclosed operation last week around the Iraqi town of Qaim, near the border with Syria.

U.S. special forces shot and captured several Syrian border guards during a firefight that broke out as the Americans attacked a convoy of suspected high-level fugitives linked to Saddam Hussein's government. They were apparently trying to cross into Syria.

An undisclosed number of people were killed and wounded in the incident, and American troops captured about 20 people, most of whom have since been released, a senior defense official said Monday. U.S. investigators will conduct DNA testing to identify the remains of those killed, defense officials said.

Three U.S. senators, in the first visit by elected American officials to Iraq, predicted Monday that a U.S. presence may be required in Iraq for as long as five years.

"I don't think the American people fully appreciate just how long we are going to be committed here and what the overall cost will be," said Senator Joseph Biden, the ranking Democrat on the Senate Foreign Relations Committee.

U.S. officials announced Monday that the defeated and dissolved Iraqi army will be re-established within a year. To start, the new army will consist of a token force of one brigade of 12,000 men. It will grow to 40,000 in three years, a tenth of the size of the Saddam Hussein-era military.

The U.S.-led occupation administration will pay a $50 to $150 monthly stipend to as many as 250,000 former Iraqi soldiers. Officers of the rank of colonel or higher and senior members of the Baath party would receive nothing, said Walter Slocombe, a senior adviser on security and defense for the governing authority.

Former soldiers from the disbanded army have been mounting increasingly vehement protests, demanding pay.