At least seven people were killed and seven wounded when a car bomb detonated during Kabul's busy morning rush hour on Wednesday, an interior ministry spokesman said.

The spokesman, Nasrat Rahimi, said the bomb had gone off in a neighbourhood which is near the interior ministry and north of Kabul airport.

He said the dead were all civilians.

"This is the initial information, more details later," he added.

A source at the interior ministry said the blast was detonated by a suicide bomber in the car, and that it had targeted a convoy of government vehicles on a main road.

The blast came one day after Afghan President Ashraf Ghani announced that Kabul would release three high-ranking Taliban prisoners in an apparent prisoner swap with Western hostages who were kidnapped by the insurgents in 2016.

The three Taliban prisoners include Anas Haqqani, who was seized in 2014 and whose older brother is the deputy Taliban leader and head of the Haqqani network, a notorious Taliban affiliate.

Ghani did not specify the fate of the Western hostages — an Australian and an American, both professors at the American University in Kabul — and it was not clear when or where they would be freed.

Ghani said on Tuesday that he hoped the decision would help "pave the way" for the start of unofficial direct talks between his government and the Taliban, who have long refused to negotiate with the administration in Kabul.