KABUL- Nine US troops were killed Tuesday after a coalition helicopter crashed in Southern Afghanistan.

According to a NATO statement, three other people, including one US civilian, were also injured in the crash.

Today’s deaths bring the total of international troops killed this year in Afghanistan to 529 according to iCasualites.org – the most in one year since the war began nine years ago. Last year 521 foreign troops were killed.

The cause of the crash is unknown and a NATO statement said it was investigating the incident. In the past, mechanical failures and enemy fire have brought down coalition helicopters.

The Taliban claimed credit for the crash, however, a NATO statement said “there were no reports of enemy fire in the area.”