KABUL, Afghanistan - Insurgents trying to escape U.S. Marines took refuge in a cave and killed two Americans during a five-hour battle in eastern Afghanistan that left an estimated 23 rebels dead, the U.S. military said Monday.

The clash, which also involved American attack planes, was the latest in a string of battles that the military says has inflicted heavy losses on militants who have intensified attacks since winter snows melted.

A U.S. statement said Sunday's battle began when a Marine unit checked on a tip about insurgents operating in Laghman, an opium-producing area 60 miles east of the capital, Kabul.

Insurgents opened fire with small arms and rocket-propelled grenades and then split into two groups, one of which fled to a village and the other to a cave on a nearby ridge, the statement said.

"U.S. Air Force A-10 aircraft engaged the insurgents in the cave and a squad of Marines went afterwards to assess the situation," it said. "The two Marines were killed while clearing the cave area."

The statement said two insurgents were confirmed dead and 21 more were thought to have been killed. There was no word on any wounded from either side.

The deaths of the two Marines brought to 143 the number of American troops killed in and around Afghanistan since the start of Operation Enduring Freedom in late 2001, according to U.S. Defense Department statistics.

After a winter lull, loyalists to the ousted Taliban regime and other militants opposed to the U.S.-backed government of Afghan President Hamid Karzai have ramped up their insurgency with a string of attacks and bombings.

But the rebels have suffered severe casualties when U.S. warplanes have caught large groups on open ground.

American commanders insist they are grinding the insurgents down and persuading villagers along the Pakistani border to stop sheltering them. They also suggest an 18,000-member U.S.-led international force could be trimmed after Sept. 18 parliamentary elections if a government reconciliation plan does well.

Karzai and U.S. officials have said the reconciliation process is open to all "non-criminal" Taliban and members of other groups. Officials say several dozen former fighters already have come forward.

The head of a peace commission supposed to oversee the process said Monday that the offer covered even Taliban leader Mullah Mohammed Omar and renegade former premier Gulbuddin Hekmatyar, both wanted as terrorists by the United States.

Sibghatullah Mujaddedi, a former Afghan president, said he would negotiate with any Afghan ready to lay down arms and recognize Karzai and Afghanistan's new democratic constitution.

A U.S. spokesman, Col.

James Yonts, said the military was studying Mujaddedi's remarks, but suggested he had gone too far.

"Our position all along has been that those guilty of serious crimes must be responsible for their actions," Yonts told The Associated Press. "We believe the government of Afghanistan understands and supports that."