A couple freed from the Taliban did not immediately board a US-bound plane from Pakistan on Thursday over the Canadian husband's concerns he might face American scrutiny for links to a former Guantanamo Bay captive, an official said.

Speaking on condition of anonymity, the US military official told AFP that Joshua Boyle and his American wife Caitlan Coleman, along with their three children, were hesitating to get on the US military jet.

In 2009, Boyle was briefly married to Zaynab Khadr, the sister of Canadian-born Omar Khadr who spent a decade at Guantanamo.

The official said Boyle did not risk any repercussions by boarding an American plane.

"It is not in our intention to do anything like that. We are prepared to bring them back home," the official said.

Boyle and Coleman were kidnapped during a backpacking trip in Afghanistan in 2012 and were held for five years, during which time they had three children.

US President Donald Trump identified their captors as the Haqqani group, whose head, Sirajuddin Haqqani, is also the Afghan Taliban's deputy leader.