KABUL, Afghanistan — A U.S. Black Hawk helicopter crashed in Kandahar province Thursday, killing seven U.S. troops and four Afghans, U.S. and Afghan military officials said.

Afghan officials said the crash site was in Shah Wali Kot, a volatile district where insurgents have long been active.

The NATO force said the cause of the crash was under investigation and was tight-lipped about whether insurgent fire had been reported in the area. Usually, the military makes a quick announcement if there is no indication the craft was brought down by enemy fire, and if factors such as weather or mechanical failure are suspected.

The Taliban claimed responsibility for bringing down the helicopter, but the group routinely boasts of shooting down any NATO aircraft that crashes.

A U.S. military officer in Afghanistan said it was possible the helicopter had been shot down.

"It's conceivable. There were enemy in the area," he said, speaking on the condition of anonymity. The UH-60 Black Hawk burned when it crashed, making it more difficult to determine the cause.

Afghan fighters were seen moving toward the crash site but were driven off by another U.S. helicopter, the officer said. The bodies of those on board were recovered, he said.

The deaths included three U.S. special-operations troops, four U.S. crew members, three Afghan special-operations soldiers and a civilian interpreter.

Kandahar is a traditional Taliban stronghold and the spiritual birthplace of the hard-line Islamist movement, which ruled Afghanistan before being ousted in 2001 by the U.S.-led alliance for sheltering al-Qaida's leaders.

The war's most lethal single incident for U.S. troops came a year ago when insurgents shot down a Chinook in Wardak province, killing all 38 aboard, including 30 Americans, many of whom were Navy SEALs.

August has been a particularly deadly month for U.S. forces in Afghanistan. Before Thursday's crash, 19 Americans had died, including seven killed last week in attacks reportedly carried out by Afghan allies.

At least 1,961 U.S. service personnel have been killed in Afghanistan during the 11-year war. Casualties rose steadily each year before reaching a peak in 2010, when 492 personnel were killed. There has been a slight decrease since then, with 398 killed in 2011, and at least 219 this year.

Material from The Associated Press is included in this report.