A roadside bomb in southern Afghanistan killed a U.S. service member Monday, while an American civilian working for the military died after insurgents attacked a patrol in the east, officials said.

The military death brings to 22 the number of U.S. troops killed in August, as foreign and Afghan forces step up their fight against the Taliban-led insurgency raging in much of the country's south and east.

A military statement would not disclose details on the latest casualties. It said only that the civilian died after insurgents attacked his patrol with gunfire.

Thousands of U.S. Marines are pushing ahead with their largest-ever operation in Afghanistan as they try to secure parts of southern Helmand province, a major Taliban stronghold.

A number of insurgent groups also operate in eastern Afghanistan, a mountainous area that borders Pakistan.

Attacks in Afghanistan have risen steadily the last three years. U.S., NATO and Afghan security forces are out in force this week to help protect voters taking part in Thursday's presidential election.