The United States said Wednesday it has made a “substantial proposal” to Russia, which people familiar with the matter described as a prisoner swap that would send convicted Russian arms trafficker Viktor Bout back to Moscow to secure the release of American professional basketball star Brittney Griner and accused spy Paul Whelan.

The proposal was made several weeks ago, in June, although nothing has come of it to date even as officials from the two governments have discussed it. But U.S. Secretary of State Antony Blinken, while declining to discuss details of the would-be deal, told reporters in Washington he expects to raise the issue yet again this week in a phone call with his counterpart, Russian Foreign Minister Sergey Lavrov.

News of a possible prisoner swap came the same day as Griner, who has admitted arriving in Russia in February with vape canisters containing cannabis oil in her luggage, testified at a court hearing that a language interpreter provided to her translated only a fraction of what was being said as authorities arrested her.

Griner, who faces up to 10 years in prison if convicted of transporting drugs, said she was instructed by officials to sign documents at the Moscow airport without them providing an explanation for what she was acknowledging. A Russian court has authorized her detention until Dec. 20.

Whelan, a former U.S. Marine, has been imprisoned in Russia for alleged espionage since 2018, with his family and Griner’s pleading with the White House to expedite efforts to gain their release.

For years, Russia has sought the release of Bout, an arms dealer once labeled the “Merchant of Death.” He was sentenced to 25 years in prison in 2012 after his conviction in a scheme to illegally sell millions of dollars in weapons.

The possible prisoner swap was approved by U.S. President Joe Biden, CNN reported, with Biden’s support overriding opposition from the Department of Justice, which is generally against prisoner trades for fear they would incentivize other governments to seize Americans overseas in hopes of prisoner swap deals of their own.

At the White House, National Security Council spokesman John Kirby declined to spell out details of the negotiations with Russia at a time the U.S. has led world opposition to Russia’s invasion of Ukraine in February.

“But I will say that the president and his team are willing to take extraordinary steps to bring our people home, as we’ve demonstrated with Trevor Reed, and that’s what we’re doing right here,” Kirby said. “It’s actively happening now. This has been the top of the mind for the president and for his whole national security team.”

The U.S. secured the release of Reed in April. He was a former Marine who was held captive in Russia for more than two years after being accused of assaulting a Russian police officer. He was traded for Konstantin Yaroshenko, a Russian pilot then serving a 20-year federal prison sentence for a cocaine smuggling conspiracy.

In the sixth session of her slow-moving trial, Griner testified Wednesday she had no criminal intent in carrying the cannabis oil into Russia. She said she still does not know how the cannabis oil for which she had a doctor’s recommendation ended up in her luggage.

She explained she had packed in haste for the 13-hour flight from the U.S. to Russia, where she was planning to play during the offseason of the Women’s National Basketball Association.

Griner said she was offered neither an explanation of her rights as she was detained nor access to lawyers to explain the documents she signed.

During a Tuesday court session, a Russian neuropsychologist testified about worldwide use of medicinal cannabis, but the drug remains illegal in Russia. Griner’s lawyers have presented a U.S. doctor’s letter recommending that she use medical cannabis to treat pain, which she says she has sustained from her basketball career.

Griner testified Wednesday that cannabis oil is widely used in the U.S. for medicinal purposes and has fewer negative effects than some other painkillers.

But a Russian Foreign Ministry spokesperson said last week that the legalization of cannabis for medical and recreational use in parts of the U.S. had no bearing on what happens in Russia.

Some material in this report came from The Associated Press and Reuters