BAGHDAD, Iraq - Four U.S. service members were killed today in an ambush in the Sunni Muslim city of Ramadi, witnesses said. Videotape delivered to Associated Press Television News showed the four, still in uniform, lying dead near what appeared to be a walled compound.

There was no immediate comment from the U.S. military command.

On Sunday, attackers lying in wait for Iraqi troops detonated a roadside bomb on the dangerous road leading to Baghdad's airport Sunday, killing two Iraqi soldiers and wounding 11. American troops took the Iraqi wounded to a U.S. aid station and waited while they were treated.

An American Marine was killed in a non-combat incident Saturday in Anbar province, which includes Ramadi and Fallujah, the U.S. military said. A mortar round also injured six police and four Iraqis in a separate attack Sunday near the Iraqi central bank in Baghdad.

Elsewhere, U.S. forces clashed with insurgents in Samarra, striking back with helicopter gunships after guerrillas fired mortars into a residential neighborhood. U.S. 1st Infantry Division spokesman Maj. Neal O'Brien said at least four insurgents were killed.

An official from a U.S.-based shipping company said today that Iraq has resumed oil exports of about 1 million barrels a day through its southern Basra terminal.

Mohammed Hadi, head of operations for Norton Lilly International's Baghdad operations, told The Associated Press by telephone from Jordan that pumping had resumed Sunday morning.

"Crude oil is being loaded onto one tanker at the rate of 42,000 barrels an hour, or about 1,008,000 barrels a day. Two other tankers are waiting for loading, and another two are in the anchorage area," Hadi said.

Key oil pipelines were damaged Tuesday and Wednesday in separate sabotage attacks, halting oil exports.

Interim Prime Minister Iyad Allawi said the Iraqi government may impose martial law in parts of the country to fight insurgents after it takes over power from the U.S.-led occupation on June 30.

Allawi also said he intends to resurrect aspects of Iraq's former military, enlarging the overall army while creating police and paramilitary units focused on controlling riots and fighting guerrillas.

"They are trying to destroy our country and we are not going to allow this," Allawi said Sunday.

He added that the May 2003 decision to disband the Iraqi army was a mistake.

The fledgling army being trained by the United States is coming under attack as Allawi's interim government prepares for the handover of sovereignty.

Allawi said his ministers were discussing the imposition of emergency law in parts of Iraq.

"We might impose some kind of martial law in some places if necessary in accordance with the law and in respect to the human rights and the international law," he said.