Afghan-Taliban conflict: Helicopters carrying wounded troops collide.
Afghan forces patrol the Helmand-Kandahar road amid clashes with the Taliban.
Tens of thousands of Afghan soldiers have been killed and injured in the past four years. This is their story.
Afghans flee their villages as fighting intensifies between Taliban militants and security forces.

A collision between two Afghan army helicopters evacuating wounded soldiers in southern Helmand province has left at least nine people dead.

All those who died were on board the helicopters, officials say.

The incident early on Wednesday in Nawa district was apparently caused by technical issues.

The area has seen fierce clashes in recent days between the Taliban and Afghan government forces, supported by US airstrikes.

The insurgents have been fighting their way to the outskirts of the nearby city of Lashkar Gah where they have already taken control of one district.

The United Nations in Afghanistan says more than 35,000 people have been forced to flee their homes in Helmand.

It's the most serious and sustained attack by the Taliban since peace negotiations began last month in Qatar, the BBC's Secunder Kermani says.