Four American soldiers and an Afghan civilian were killed Tuesday by a roadside bomb in southern Afghanistan.

The U.S. military said the troops were on patrol with Afghan security forces when their vehicle hit a bomb.

The military did not say exactly where the bombing occurred.

Twenty-nine American troops have died in Afghanistan this year, far surpassing the eight killed in the first two months of 2008.

Roughly 38,000 American soldiers are serving in Afghanistan, along with about 30,000 troops in a NATO-led force.

More than 2,500 Canadians are part of the NATO mission, with the bulk serving in the southern Kandahar province, where the Taliban insurgency has been active. Since the mission started seven years ago, 108 Canadian soldiers and one diplomat have been killed.

American, British and Dutch troops are also in the south.

U.S. President Barack Obama recently ordered 17,000 more American soldiers deployed to Afghanistan as his administration shifts its military focus from Iraq to Afghanistan.

In a separate incident in southern Helmand province Monday, coalition and Afghan forces killed 16 militants when responding to gunfire from insurgents on their convoy, the U.S. said in another release.

There were no other reports of casualties, the statement said.