The diplomat, who spoke to reporters on condition of anonymity, declined to provide details about why the planned exchange, which Afghan President Ashraf Ghani announced on Tuesday, did not occur.
The U.S. State Department did not immediately respond to a request for comment, nor did the Afghan and Australian embassies in Washington.
The Afghan government’s decision to free Anas Haqqani and two other Taliban commanders, Haji Mali Khan and Hafiz Rashid, was taken in the hope of securing direct talks with the Taliban, which has refused to engage with what it calls an illegitimate “puppet” regime in Kabul. All three were captured in 2014.
In return U.S. citizen Kevin King and Australian citizen Timothy Weeks, professors kidnapped by the Taliban in August 2016 from the American University of Afghanistan in Kabul, were to be freed.