KABUL, Afghanistan — A NATO helicopter was shot down by hostile fire today in southern Afghanistan, killing four American troops, NATO and the U.S. military said.

Taliban spokesman Qari Yousef Ahmadi said the insurgents shot off two rockets to down the helicopter.

The attack occurred about midday in the Sangin district of Helmand province, provincial government spokesman Daoud Ahmadi said.

Lt. Col. Joseph T. Breasseale, U.S. military spokesman in Kabul, confirmed the four troops killed were Americans.

U.S. troops have been building in southern Afghanistan — the Taliban's heartland — as part of President Barack Obama's surge strategy to try to end the nearly nine-year-old insurgency.