KABUL -- U.S. envoy to Afghanistan Zalmay Khalilzad has departed to Qatar to discuss with the Taliban the "current challenges" in implementing a peace deal signed by the United States and the militant group in late February, the State Department says.

The April 13 announcement comes after an initial prisoner exchange between the Taliban and the Afghan government that was hailed by Khalilzad as an "important step" toward peace.

The ambassador, who negotiated the U.S.-Taliban deal, departed on April 12 for talks with Taliban representatives in the Qatari capital, Doha, where the militants have a political office, a statement said.

According to the International Committee of the Red Cross, the Taliban on April 12 released 20 Afghan prisoners in the southern province of Kandahar.

The move came after the Afghan government released 100 Taliban prisoners, bringing to 300 the total number of Taliban inmates freed since April 8.

Khalilzad on April 13 urged both sides to "accelerate efforts to meet targets specified in the U.S.-Taliban agreement as soon as possible," adding that the exchange was more important than ever with prison populations threatened by an outbreak of coronavirus.

The pact signed by the United States and the Taliban in Doha on February 29 calls for the Afghan government to release 5,000 Taliban fighters as a confidence-building measure ahead of formal peace talks aimed at ending the 18-year conflict in Afghanistan.

The Taliban has vowed to release some 1,000 Afghan government troops and civilian workers it is holding.

But the Taliban last week recalled a three-member team it had sent to Kabul to try to finalize the swap originally set to happen by March 10.

The militants blamed the administration of Afghan President Ashraf Ghani for delaying the exchange "under one pretext or another,” while Kabul called on the Taliban not to “sabotage the process by making excuses."

On April 12, the Taliban told AFP that their decision to release a first group of prisoners was "a goodwill step...to accelerate the prisoner exchange process."

In return for the start of talks between Kabul and the Taliban and a series of security commitments from the militants, all U.S. troops and other foreign coalition forces are meant to withdraw from Afghanistan within 14 months.

With reporting by AFP