Kabul, Afghanistan ? Fighting sparked by an insurgent attack on patrolling coalition forces in southern Afghanistan killed one U.S. service member and at least 16 suspected Taliban rebels, amid spiraling violence ahead of key legislative elections, the military said Tuesday.

The American – the fourth U.S. casualty in less than a week – was killed when militants opened fire with small arms and rocket-propelled grenades on Afghan and U.S. forces Monday in Zabul province’s Day Chopan district, a remote and mountainous region known as a hub of rebel activity.

U.S. and coalition aircraft joined the ensuing battle. The American military said in a statement that “initial estimates indicate at least 16 enemy forces were killed.” It gave no further details about the U.S. casualty, pending notification of relatives.