WASHINGTON: Six US troops were killed Tuesday in a helicopter crash in southern Afghanistan, US defense officials told AFP.

The helicopter went down in Zabul province and an investigation was underway to determine “the cause of engine failure,” said a US defense official, who spoke on condition of anonymity.

“I can confirm six Americans were killed,” said the official.

There was no indication enemy fire brought down the aircraft, the official added.

The last fatal helicopter incident for US forces occurred in April, when an Apache chopper went down in eastern Afghanistan, claiming the lives of two American troops.

There are currently 42,700 US troops deployed in Afghanistan as part of a Nato-led force that is due to withdraw by the end of 2014.

A smaller US-led contingent is due to stay in the country pending the signature of a security agreement between Washington and Kabul.