WASHINGTON (AFP) — American basketball star Brittney Griner was headed back to the United States after being released from a Russian prison in exchange for an arms dealer known as the "Merchant of Death."

Griner, 32, who was arrested in Russia in February on drug charges, and Viktor Bout, 55, who was serving a 25-year sentence in a US prison, were exchanged at an airport in Abu Dhabi.

In footage released by Russian state media, Griner, shorn of her distinctive dreadlocks, and a relaxed and animated Bout could be seen crossing paths on the airport tarmac and heading towards the planes that would take them home.

President Joe Biden announced Griner's release early Thursday in an address to the nation at the White House.

"She is safe. She is on a plane. She is on her way home," he said.

The President said he had spoken to her and she was in "good spirits" after suffering "needless trauma."

Griner, a two-time Olympic gold medalist, Women's National Basketball Association champion and LGBT trailblazer, was arrested at a Moscow airport nine months ago against a backdrop of soaring tensions over Ukraine.

She was accused of possession of vape cartridges with a small quantity of cannabis oil and sentenced in August to nine years in prison.

Bout, who was accused of arming rebels in some of the world's bloodiest conflicts, was detained in a US sting operation in Thailand in 2008, extradited to the United States and sentenced in 2012 to 25 years behind bars.

He landed in Russia on Thursday, state television said.

"Don't worry, everything is okay, I love you very much," he told his mother Raisa.

While Griner's family and friends celebrated her release, another American held in Russia, Paul Whelan, a former US Marine detained since 2018 and accused of spying, was not part of Thursday's exchange and he told CNN he was "greatly disappointed."

"I don't understand why I'm still sitting here," Whelan told the US television network in a phone call from the Russian penal colony where he is imprisoned.

Biden pledged to obtain Whelan's freedom, saying "we will never give up."

"Sadly, for totally illegitimate reasons, Russia is treating Paul's case different than Brittney's," he said.

As for Griner's release, Biden said "this is a day we've worked toward for a long time. It took painstaking and intense negotiations."