The exchange of three senior Taliban prisoners for two foreign hostages announced by Afghan President Ashraf Ghani has been delayed, a spokesman said on Saturday.
The Taliban prisoners "are still being held by the Afghan government. The inability of the Taliban to meet the conditions has caused a delay in the exchange," Ghani's spokesman Sediq Sediqqi wrote on Twitter.
The government "will review the exchange process in light of Afghanistan's national interests," he said, without providing further details.
Ghani announced the exchange on Tuesday, saying the Taliban prisoners held at Bagram prison would be "conditionally" released.
They 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.
The two foreign hostages -- American Kevin King and Australian Timothy Weeks -- were kidnapped by gunmen wearing military uniforms in Kabul in August 2016.
Ghani said, "their health has been deteriorating while in the custody of the terrorists".
He added the release of the two men, both professors, would "pave the way" for the start of unofficial direct talks between his government and the Taliban, who long have refused to negotiate with Ghani's administration.