An armed clash in central Afghanistan has left one U.S. Marine dead and another injured. The fighting comes amid efforts by neighboring Pakistan to root out Afghan militants hiding on its territory.

U.S. forces in Afghanistan say the attack occurred early Saturday in the mountainous central province of Uruzgan.

A military spokesman, Lieutenant Colonel Tucker Mansager, said the Marines were attacked during a night patrol south of the provincial capital of Tarin Kot.

"It was as the result of direct fire engagement with anti-coalition militias in the area," he said. "The attack did not occur against the Marine base. These people were out on a mission away from their base when the attack occurred."

He said attacks by anti-government insurgents had become more frequent over the past month. But he added that U.S. forces in Afghanistan had increased over the same period, from a level of 15,000 to about 20,000.

While some of the increase is due to an overlap of forces as troops are rotated out of the country, the larger size also includes a Marine "surge force" meant to bolster the U.S. military presence.

U.S. and Afghan government forces are seeking to contain the anti-government militias as the country prepares for its first election in almost two decades, currently scheduled for September.

Lieutenant Colonel Mansager also voiced support for Pakistan's efforts to track down Afghan and other foreign militants believed hiding on the Pakistani side of the border.

Pakistan is currently negotiating the surrender of an estimated several hundred foreign militants, including members of the al-Qaida terror network, said to be based in the country's semi-autonomous tribal area.

As talks between Pakistani officials and local tribal representatives continue, Pakistan has again extended the deadline for the militants to turn themselves in.

The U.S. military spokesman said his forces are cooperating closely with their Pakistani counterparts in order to flush out the Afghan insurgents.

"We continue to maintain robust forces down in that border area and continue to coordinate closely with the Pakistan military on the other side," said Lt. Colonel Mansager.

The majority of the anti-government forces are remnants of Afghanistan's former Taleban regime, ousted in 2001, which opposes both the planned election and the U.S. troop presence.