Image copyright PA Image caption The accident involved a Puma Mk2 helicopter (file picture)

Five people, including two RAF personnel, have been killed in a helicopter crash in Afghanistan.

The Puma Mk2 helicopter crashed as it was landing at Nato's training and support mission HQ, in Kabul. Nato has not released the nationalities of the other victims or the five left injured.

A Ministry of Defence spokesman said the crash was "an accident and not the result of insurgent activity".

Defence Secretary Michael Fallon expressed his "deepest sympathies".

The MoD said the families of the British victims had asked for a period of grace before their names were released.

The accident comes after a convoy of UK military vehicles was attacked in Kabul, the Afghan capital, on Sunday morning, injuring seven people. There were no UK casualties, the MoD said.

The MoD said an improvised explosive device caused an explosion, while officials in Kabul said it was a suicide bombing.

The Taliban said it carried out the attack in retaliation for air strikes in Kunduz that killed civilians and doctors.

'Hostile environment'

The two RAF personnel killed in the helicopter crash were from 230 and 33 squadrons, both of which are based at RAF Benson, in Oxfordshire, the MoD spokesman said.

He added: "The incident is currently under investigation but we can confirm that it was an accident and not the result of insurgent activity."

Image copyright AFP Image caption Nato troops examine a crater at the site of the bomb attack that targeted a UK convoy of military vehicles

Mr Fallon said it was a "stark reminder that our brave service personnel continue to work night and day in a hostile and challenging environment.

"This is a very sad time for the men and women of RAF Benson and UK personnel in Afghanistan.

"Although the UK's combat mission has ended, the dedication and professionalism of our men and women is essential as we continue to support the government of Afghanistan as they seek to build a peaceful and prosperous future for their country."

'Observation balloon'

BBC defence correspondent Jonathan Beale said the BBC understood that the RAF Puma that crashed in Kabul had been transferring Nato military personnel.

"Helicopter movements of military personnel are more frequent following attacks - such as the one that took place on a British military convoy earlier on Sunday.

"The cause of the crash is still being investigated but an observation balloon became untethered and landed in the resolute support base in Kabul."

An Afghan eyewitness said the helicopter appeared to strike the balloon as it landed at the base.

The helicopter "hit the cable of the security balloon over the base," he said.

"It seemed like the cable was turned around the helicopter rotor."

An observation balloon is used as an aerial platform for gathering information and spotting aircraft.

British combat troops pulled out of Afghanistan a year ago after a conflict that had lasted 13 years and in which 454 UK troops lost their lives.

Nato's resolute support mission, which was launched after its combat mission ended, consists of more than 13,000 troops from 42 countries, including nearly 500 UK troops.

It focuses on training and supporting Afghan security forces and institutions.