Maj. Gen. Richard Felton, commander of the Joint Helicopter Command, said the crash was likely "a tragic accident."
"We can confirm that a UK helicopter crashed in southern Afghanistan today," said the British Ministry of Defense in a statement. "The incident is under investigation and it would be inappropriate to comment further until families have been notified."
The helicopter was carrying soldiers from the International Security Assistance Force (ISAF) and crashed due to technical problems, an Afghan official said.
"'ISAF is still in the process of reviewing the circumstances to determine more facts,' ISAF said. It did not provide details of their nationalities."
Zia Durrani, a Kandahar provincial police spokesman, said the helicopter crashed in the Takhta Pul district in the southeast, about 31 miles from the Pakistani border.
"Today, the mujahedeen hit the foreign forces' helicopter with a rocket, and 12 soldiers on board were killed," spokesman Qari Yousef Ahmadi said. The insurgents frequently exaggerate death tolls in their attacks and falsely have claimed responsibility for incidents before.
Saturday's helicopter crash was the single deadliest incident this year for foreign forces and brings the death toll to seven this month.
The last deadliest day for coalition forces was Dec. 17, 2013, when a helicopter crash killed six U.S. service members.
According to an Associated Press count, 23 have been killed this year, a much lower number than in previous years.
NATO forces are preparing to withdraw troops from Afghanistan at the end of this year, 13 years after the U.S. invaded Afghanistan after the Taliban provided shelter for Osama bin Laden and other al-Qaida leaders.
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