A helicopter crash in southern Afghanistan has killed five US service members, officials have said.

The helicopter went down outside Kandahar city, the capital of Kandahar province, last night.

The NATO military coalition said in a statement that "initial reports" showed no enemy activity in the area at the time.

The cause of the crash is under investigation.

A US official, speaking on condition of anonymity, said all five of the dead were American.

The crash came on the same day that two US troops and five Afghan police and soldiers were killed in a so-called insider attack by a person in an Afghan military uniform in the east of the country.

New US Defense Secretary Chuck Hagel left Afghanistan earlier yesterday after a difficult first trip to Kabul.

His trip was marred by a suicide bomb attack near where he was holding a meeting, and differences with Afghan President Hamid Karzai, who accused the US of colluding with the Taliban.

Last August, 11 people, including seven US soldiers, were killed when a Black Hawk helicopter crashed in southern Afghanistan.

The worst such incident was in August 2011, when the Taliban shot down a CH-47 Chinook transport helicopter, killing all 38 people on board, including 25 US special operations troops.