WASHINGTON (AP) — Russia freed WNBA star Brittney Griner on Thursday in a dramatic high-level prisoner exchange, with the U.S. releasing notorious Russian arms dealer Viktor Bout, American and Russian officials said. The swap, at a time of heightened tensions over Ukraine, achieved a top goal for President Joe Biden, but carried a heavy price — and left behind an American jailed for nearly four years in Russia.

The deal, the second such exchange in eight months with Russia, procured the release of the most prominent American detained abroad. Griner is a two-time Olympic gold medalist whose monthslong imprisonment on drug charges brought unprecedented attention to the population of wrongful detainees.

Biden’s authorization to release a Russian felon once nicknamed “the Merchant of Death” underscored the escalating pressure that his administration faced to get Griner home, particularly after the recent resolution of her criminal case and her subsequent transfer to a penal colony.

The swap was confirmed by U.S. officials with direct knowledge of the negotiations who were not authorized to publicly discuss the deal before a White House announcement and spoke on condition of anonymity. Biden spoke with Griner on the phone Thursday while her wife, Cherelle, was in the Oval Office. The president was to address reporters later in the morning.

“Moments ago I spoke to Brittney Griner. She is safe. She is on a plane. She is on her way home,” Biden tweeted.

The Russian Foreign Ministry also confirmed the swap, saying in a statement carried by Russian news agencies that the exchange took place in Abu-Dhabi and that Bout has been flown home

Russian and U.S. officials had conveyed cautious optimism in recent weeks after months of strained negotiations, with Biden saying in November that he was hopeful that Russia would engage in a deal now that the midterm elections were completed. A top Russian official said last week that a deal was possible before year’s end.

Even so, the fact that the deal was a one-for-one swap was a surprise given that U.S. officials had for months expressed their their determination to bring home both Griner and Paul Whelan, a Michigan corporate security executive jailed in Russia since December 2018 on espionage charges that his family and the U.S. government has said are baseless.

In releasing Bout, the U.S. freed a a former Soviet Army lieutenant colonel whom the Justice Department once described as one of the world’s most prolific arms dealers. Bout, whose exploits inspired a Hollywood movie, was serving a 25-year sentence on charges that he conspired to sell tens of millions of dollars in weapons that U.S officials said were to be used against Americans.

The Biden administration was ultimately willing to exchange Bout if it meant Griner’s freedom. The detention of one of the greatest players in WNBA history contributed to a swirl of unprecedented public attention for an individual detainee case — not to mention intense pressure on the White House.

Griner’s arrest in February made her the most high-profile American jailed abroad. Her status as an openly gay Black woman, locked up in a country where authorities have been hostile to the LBGTQ community, infused racial, gender and social dynamics into her legal saga and made each development a matter of international importance.

Her case not only brought unprecedented publicity to the dozens of Americans wrongfully detained by foreign governments, but it also emerged as a major inflection point in U.S.-Russia diplomacy at a time of deteriorating relations prompted by Moscow’s war against Ukraine.

The exchange was carried out despite deteriorating relations between the powers. But the imprisonment of Americans produced a rare diplomatic opening, yielding the highest-level known contact between Washington and Moscow — a phone call between Secretary of State Antony Blinken and Russian Foreign Minister Sergey Lavrov — in more than five months.

In an extraordinary move during otherwise secret negotiations, Blinken revealed publicly in July that the U.S. had made a “substantial proposal” to Russia for Griner and Whelan. Though he did not specify the terms, people familiar with it said the U.S. had offered Bout.

Such a public overture drew a chiding rebuke from the Russians, who said they preferred to resolve such cases in private, and carried the risk of weakening the U.S. government’s negotiating hand for this and future deals by making the administration appear too desperate. But the announcement was also meant to communicate to the public that Biden was doing what he could and to ensure pressure on the Russians.

Besides the efforts of U.S. officials, the release also followed months of backchannel negotiations involving Bill Richardson, the former U.S. ambassador to the United Nations and a frequent emissary in hostage talks, and his top deputy Mickey Bergman. The men had made multiple trips abroad in the last year to discuss swap scenarios with Russian contacts.

Griner was arrested at the Moscow’s Sheremetyevo Airport in February when customs officials said they found vape canisters with cannabis oil in her luggage. She pleaded guilty in July, though still faced trial because admitting guilt in Russia’s judicial system does not automatically end a case.

She acknowledged in court that she possessed the canisters, but said she had no criminal intent and said their presence in her luggage was due to hasty packing.

Before being sentenced on Aug. 4 and receiving a punishment her lawyers said was out of line for the offense, an emotional Griner apologized “for my mistake that I made and the embarrassment that I brought on them.” She added: “I hope in your ruling it does not end my life.”

Her supporters had largely stayed quiet for weeks after her arrest, but that approach changed in May once the State Department designated her as unlawfully detained. A separate trade, Marine veteran Trevor Reed for Konstantin Yaroshenko, a Russian pilot convicted in the U.S. in a cocaine trafficking conspiracy, spurred hope that additional such exchanges could be in the works.

Whelan has been held in Russia since December 2018. The U.S. government also classified him as wrongfully detained. He was sentenced in 2020 to 16 years in prison.

Whelan was not included in the Reed prisoner swap, escalating pressure on the Biden administration to ensure that any deal that brought home Griner also included him.