Two Afghan army helicopters collided while evacuating wounded soldiers in southern Helmand province, nine people have died.
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.
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.
It’s the most serious and sustained attack by the Taliban since peace negotiations began last month in Qatar.
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.
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.