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.
So far discussions have been bogged down in attempts to finalise a set of rules and procedures governing the talks – and negotiators are yet to broach the broader issues of a ceasefire and possible power sharing arrangement.
Earlier this week, the head of Nato forces in Afghanistan, US General Scott Miller, condemned the Taliban for undermining the peace talks and violating the agreement they signed with the US in February.
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Large parts of Helmand and neighbouring Kandahar remain without electricity after the Taliban attacked a power substation on Monday.
A number of telecommunication networks have also been shut down.
Of about 5,000 families estimated to have been displaced, some are reported to have sought refuge in homes and properties in neighbouring areas.
One family told the BBC that they left their home in Lashkar Gah with only the clothes they were wearing, without knowing if they would find a safe place to sleep.
Others say they fear they may die from hunger, while staff at local hospitals said they had admitted dozens of casualties.
The historic peace talks began on 12 September, one day after the 19th anniversary of the deadly 9/11 al-Qaeda attacks in the US that led to the US beginning military operations in Afghanistan.
It was the first time that Afghan leaders had sat down with members of the militant Islamist group.
But correspondents say Taliban actions on the battlefield are again raising questions about their commitment to the negotiating table.
The militants say they are only taking back areas they once controlled.