KABUL, Afghanistan – A U.S. military helicopter crashed during a firefight with insurgents in a remote area of southern Afghanistan on Thursday, killing seven Americans and four Afghans in one of the deadliest air disasters of a war now into its second decade. The Taliban claimed it gunned down the Black Hawk.

American service personnel are dying at a rate of about one per day so far this year despite a drawdown of troops and dwindling attention on the home front. That death rate has risen recently with the summer fighting season in full gear and a rash of attacks by Afghan security forces on their foreign trainers and partners.

NATO forces said they could not confirm what caused Thursday’s crash and stressed that it was still being investigated. The Black Hawk was operating in support of an ongoing assault on the ground but initial indications were that it was not shot down, according to U.S. officials who spoke anonymously.

Taliban spokesman Qari Yousef Ahmadi said insurgent fighters struck the helicopter in Kandahar province Thursday morning. He declined to give further details.

The Kandahar provincial government backed the Taliban claim. It said the helicopter was shot down in Shah Wali Kot district, a rural area north of Kandahar city where insurgents move freely and regularly launch attacks. Provincial spokesman Ahmad Jawed Faisal did not provide details or say how the province had confirmed the information.

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

Thursday’s crash came less than a week after six American service members were gunned down, apparently by two members of the Afghan security forces they were training to take over the fight against the insurgency.

White House spokesman Jay Carney said Thursday that the United States is prioritizing efforts to prevent more of these types of attacks. NATO says that 34 international service members have been killed in attacks by Afghan security forces or militants wearing their uniforms so far this year.

The international force “is continually assessing and refining procedures in force protection so that we can both meet mission requirements and ensure the safety of our forces,” Carney said.