KABUL — The Taliban have released a US engineer they had held hostage since 2020 in exchange for an Afghan tribal leader held in US custody since 2005.

Mark Frerichs was handed over at Kabul airport on Monday, the Taliban said.

In return, they received Bashir Noorzai, a Taliban ally serving a life sentence for drug trafficking.

There was no immediate word from the US government or the family of Frerichs. Securing his freedom was an election pledge of President Joe Biden.

"Today Mark Frerichs was handed over to the US and Haji Bashir was handed over to us at Kabul airport," said Taliban acting foreign minister Amir Khan Muttaqi.

Frerichs, 60, was abducted by the Taliban the year before the group swept back to power in Afghanistan and its Western-backed government collapsed.

He had been living and working in Kabul as a civil engineer for 10 years.

The detention of the former navy veteran has been a major impediment to improving relations between the US and the Taliban, whose government is still to be recognized by any country in the world.

Bashir Noorzai was given a hero's welcome on his return to the Afghan capital, and was greeted by Taliban fighters carrying garlands of flowers.

"My release together with that of an American will make peace between the countries," he told a news conference.

Noorzai was a close ally and friend of Taliban founder Mullah Omar and helped finance the first Taliban government in the 1990s.

He did not hold an official position but "provided strong support including weapons", Taliban spokesman Zabihullah Mujahid told the AFP news agency.

Noorzai had served 17 years in US custody for heroin smuggling - prosecutors said he ran a vast opium-growing operation in Kandahar province, the Taliban's traditional heartlands in the south of the country.

At the time of his arrest in 2005, he was considered one of the biggest drug dealers in the world, controlling more than half of Afghanistan's drug exports, which account for most of the world's harvest.

In 2008, he was convicted by a court in New York of conspiring to smuggle more than $50m of heroin into the United States. — BBC