US President Joe Biden says Washington won't consider Taliban's legitimacy until Navy veteran Mark Frerichs is released by the group.

Biden said in a statement on Sunday that “The Taliban must immediately release Mark before it can expect any consideration of its aspirations for legitimacy”.

He said, “Threatening the safety of Americans or any innocent civilians is always unacceptable, and hostage-taking is an act of particular cruelty and cowardice”.

He addressed all the Americans being held hostage and wrongfully detained overseas, and their families and friends, saying, “Know that my administration will continue to work steadfastly until every American being unjustly held against their will comes home”.

However, Biden did not mention several hostages who are being held by the Islamic Republic of Iran despite calls by human rights organizations on the Biden Administration to press Tehran for their release during the Vienna nuclear negotiations.

Earlier in January, two former Iran hostages staged a hunger strike at the venue of the talks to revive the 2015 nuclear deal, hoping that their campaign can stop the United States from concluding a deal with Iran until the hostages are freed.

The US Special Envoy for Iran Robert Malley met with Barry Rosen, a US diplomat who was held hostage in the US embassy takeover in the early 1980s and stressed the importance of the release of four American-Iranians held in Iran but stopped short of saying their freedom was a precondition for Washington for reaching a nuclear deal with Iran.