Kabul, Afghanistan ? Afghan human rights activists warned Saturday that allegations that an American security contractor killed his Afghan interpreter could hurt the image of the United States here – even as the U.S. military suffers its deadliest year yet fighting Taliban rebels.

Underscoring the danger, militants firing rocket-propelled grenades killed a U.S. soldier and wounded another during combat operations Friday near the southern city of Kandahar, the military said. The death brought to 198 the number of U.S. service members killed in or around Afghanistan since the ouster of the unpopular Taliban regime in late 2001.

Relatives of the slain interpreter, 37-year old Noor Ahmad, threatened to set themselves on fire unless his American supervisor is tried for his death, which occurred at a compound of U.S. Protection and Investigations in western Farah province. U.S. Embassy spokesman Lou Fintor told The Associated Press that it was “our understanding that this American citizen is no longer in Afghanistan.”

The case has raised questions about the reach of Afghanistan’s fledgling legal system and law enforcers.

Foreigners working on civilian projects are generally subject to Afghan law, but the legal status of security contractors appears unclear. U.S. military personnel in Afghanistan come under American military jurisdiction.