Two separate assaults on U.S.-led forces in Afghanistan killed 11 rebels, a U.S. service member and an Afghan soldier, the U.S. military said Monday.

The latest violence comes amid fears that crucial legislative elections in September may be threatened by an upsurge in militant attacks, which have left more than 750 people dead since March.

In fighting Monday, rebels attacked a patrol in southern Uruzgan province (search), setting off a gunbattle that killed the American soldier, the Afghan soldier and the 11 rebels, as well as wounding three U.S. troops and an Afghan soldier, a military statement said.

U.S. fighter jets and attack helicopters responded to the assault, it said. Eight insurgents were captured.

"This tragic loss strengthens our resolve to further the advance of a democratic Afghanistan," said U.S. Army Brig. Gen. Jack Sterling (search), deputy commanding general of Combined Joint Task Force-76 (search).

The death brings to 173 the number of U.S. troops killed in and around Afghanistan since Operation Enduring Freedom began in 2001. The latest death came a day after another U.S. service member was killed in a firefight in neighboring Helmand province.

On Sunday, a roadside bomb wounded six U.S. service members traveling in a convoy in eastern Kunar province. Militants then fired on the vehicles before fleeing when U.S. aircraft and artillery fired back, a separate U.S. military statement said.

It was not immediately known whether any enemy fighters were killed or wounded, it said.

The attacks occurred in the same mountainous area where last month a commando team was ambushed, leaving three Navy SEALs dead, and a special forces helicopter was shot down, killing all 16 troops on board.

Sunday's attack was the first major assault on U.S. forces in Kunar since then, and may indicate that many of the militants who had been thought to have fled across the border into neighboring Pakistan after the violence in June have sneaked back into Afghanistan.

Usama bin Laden and the reclusive Taliban leader Mullah Mohammed Omar are among those believed to be sheltering along the Afghan-Pakistan frontier.

American military officials and Afghan authorities said they are investigating the authenticity of a cassette recording of a man claiming to be the fugitive Taliban chief.

Afghan Defense Ministry spokesman Gen. Mohammed Saher Azimi said the government suspects the recording is fake.

U.S. military spokesman Lt. Col. Jerry O'Hara said the armed forces do not have a copy of the recording by the man claiming to be Omar, but said the military was checking on it. The CIA declined to comment.

In a telephone interview with The Associated Press, purported Taliban spokesman Mullah Latif Hakimi played the tape, but the voice on it was garbled and unrecognizable. He then read out the comments.

"This cassette proves that I am alive and was not killed in bombings," Hakimi cited Omar as saying. "The leaders of the Taliban must unite and consult each other regarding the holy war. Our fight against the non-Muslims will be successful."

Hakimi said Omar made the recording in Afghanistan, but declined to say when.

Information from Hakimi in the past has sometimes proven exaggerated or untrue, and his exact tie to the Taliban leadership cannot be independently verified. Earlier this month, Hakimi claimed one of the SEALs in the downed helicopter had been captured alive and beheaded. The U.S. military said the SEAL died in fighting.