The strike in the western province of Herat on Wednesday drew condemnation from a top US diplomat and underscores the worsening violence in Afghanistan's war even as the Taliban and Kabul are supposed to be preparing for peace talks.

According to Ali Ahmad Faqir Yar, the district governor in the area where the strike took place, a group had gathered to welcome the Taliban commander.

"An air strike was carried out during the ceremony and civilians who participated were among those killed," he told AFP, putting the toll at eight civilian dead and 16 wounded.

Zalmay Khalilzad, the US special envoy to Afghanistan, said photographs and witness accounts indicated that many civilians, including children, had been killed.

"We urge all sides to contain the violence, protect civilians, and show necessary restraint as the start of intra-Afghan negotiations is so close," he said on Twitter.

The defence ministry, however, disputed both accounts and said none of those killed were civilians.

Afghan forces had carried out the strike "based on intelligence photos and videos", the ministry said.

"The defence ministry's investigation is ongoing, but initial information shows that no civilians were killed," it said.

It was not immediately clear if the commander had survived the attack or how many insurgents were killed or wounded.

On their website, the Taliban said the insurgent had been released from Bagram prison outside Kabul on Tuesday.

He had been freed under a contentious prisoner swap that is seen as a crucial step toward eventual peace talks.

The exchange, outlined in a deal between the Taliban and the US in February, will see the Afghan government release 5,000 insurgents while the Taliban free 1,000 Afghan security force captives.

Kabul has protested that many among the Taliban inmates being released are dangerous fighters who will return to the battlefield.

In a separate incident in the eastern province of Nangarhar on Wednesday, at least 31 Taliban fighters were killed in clashes with security forces, the defence ministry said.

In a series of tweets, the United Nations Assistance Mission in Afghanistan warned of a "spiralling cycle of violence", and mission head Deborah Lyons called for a ceasefire over the upcoming Eid festival.

In recent months, violence levels have soared in Afghanistan, with the Taliban carrying out near-daily attacks against security forces.

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