The Taliban said it would on Sunday release the first prisoners in a delayed exchange deal with the Afghan government -- a potential breakthrough after the insurgents walked out of talks with Kabul last week.

The announcement comes as fears rose that an avenue for fragile peace talks between the two sides was being undercut by mounting disagreements over the prisoner swap, considered key to paving the way for negotiations.

"Today, 20 prisoners of the Kabul administration will be released," Taliban spokesman Suhail Shaheen said on Twitter, adding that the group would be handed over to representatives of the Red Cross in the southern city of Kandahar.

The Afghan government has pressed ahead with freeing hundreds of Taliban prisoners over the past week, despite complaints from the insurgent group about the piecemeal nature of the releases.

Washington signed a landmark deal with the Taliban in February that promised the withdrawal of US and foreign troops from Afghanistan by next summer, provided the militants start talks with Kabul and adhere to other guarantees.

The deal requires the Afghan government -- which was not a signatory to the accord -- to free up to 5,000 Taliban prisoners, and for the militants to release 1,000 pro-government captives in return.

The exchange was supposed to have happened by March 10, allowing peace talks to begin, but has been beset with problems.

Kabul has claimed the Taliban want 15 of their "top commanders" to be released, while the insurgents have accused Afghan authorities of needlessly wasting time.

A small Taliban team met with the government to discuss a comprehensive prisoner swap last week, but walked out of the talks soon after officials offered a gradual release of the prisoners.

Sunday's announcement came after the head of US and NATO forces in Afghanistan met with insurgent leaders to discuss a reduction in violence in the war-weary country. 

The Taliban cautioned that their decision to release a group of prisoners did not mean that the talks with Kabul were being restarted. 

"No the process is not back on, but this is a good will step by the [the Taliban] to accelerate the prisoners exchange process," insurgent spokesman Zabihullah Mujahid told AFP.

Javid Faisal, the spokesman for the Afghan National Security Council, chided the insurgents for not starting the process earlier, saying a reduction in violence and subsequent ceasefire between the two sides was needed. 

"They should also prepare for a face-to-face meeting with the Islamic republic of Afghanistan," said Faisal. 

The insurgents have also stepped up their attacks on Afghan security forces in government-controlled areas across the country and accused US forces of aiding the Afghan government with air support, causing civilian casualties.