NATO is confirming that the six troops killed in roadside bombing in Afghanistan on Sunday were Americans.

Brig. Gen. Gunter Katz, a spokesman for the U.S.-led coalition, disclosed their nationalities at a briefing on Monday. He said he could not provide other details about the incident because it is still under investigation. The Taliban have claimed responsibility for the bombing.

The service members' deaths were the latest caused by bombs planted by insurgents along roads, paths or mountain tracks.

A surge in Afghan and coalition forces during the past two years has routed Taliban fighters from many of their strongholds in the south, but the insurgents have stepped up their attacks this summer to take back key areas.