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 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 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.