The Afghan government will gradually release 5,000 Taliban prisoners starting this week if the insurgents significantly reduce violence, President Ashraf Ghani's spokesman said Wednesday, paving the way for peace talks following a US withdrawal deal.

The government will "release 1,500 Taliban prisoners as a gesture of goodwill" starting Saturday, with another 3,500 to be freed after negotiations begin, Sediq Sediqqi said on Twitter.

The release will depend on the Taliban's willingness to significantly limit attacks in the country, he added.

The decision attempts to resolve one of the key disputes between the insurgents and the Afghan government.

Although the Taliban were due to start talks with Kabul on Tuesday, negotiations were delayed because the insurgents had demanded the release of 5,000 prisoners in return for 1,000 captives as a prerequisite for talks.

Ghani had refused to accede but Wednesday's decree signalled a softening of his stance, with the proviso that none of the released prisoners would return to the frontlines.

The prisoner exchange was one of the key points in a US-Taliban agreement signed in Qatar last month. 

Under the terms of that deal, foreign forces will quit Afghanistan within 14 months, subject to Taliban security guarantees and a pledge by the insurgents to hold talks with Kabul.