The White House said Monday that the Biden administration is "bound and determined" to bring Marine veteran Paul Whelan home to the United States, and insisted that President Joe Biden’s "commitment" to the effort is "absolutely rock solid, intense" and "as high a priority as the president has."

Whelan, a U.S. Marine veteran who remains in a Russian prison, has been detained since December 2018 for espionage charges that his family and the United States have said are baseless.

White House national security adviser Jake Sullivan on Monday took the podium at the press briefing to announce that members of the National Security Council and the State Department met virtually with Whelan’s wife, Elizabeth, earlier in the day.

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Paul Whelan, a U.S. Marine veteran who was arrested for alleged spying, listens to the verdict in a courtroom in Moscow, Russia, June 15, 2020. (Sofia Sandurskaya, Moscow News Agency photo via AP, File)

"You’ll understand that I can’t get into the specifics of the kinds of things that we are contemplating to try to ensure that we get Paul home as soon as we can," Sullivan said, adding that conversations with the Whelan family "have been substantive."

"We have been working to figure out what it is going to take to ultimately secure his freedom and how we can go about getting that, and being able to sit down with the Russians and work out a deal," Sullivan said. He added that specifics on the efforts "really have to be kept in the sensitive channels" the United States has with the Russian government.

"But we are bound and determined to ensure that we work through a successful method of securing Paul Whelan’s release at the earliest possible opportunity," he said.

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Jake Sullivan Russia Paul Whelan

White House national security adviser Jake Sullivan speaks at a press briefing at the White House, Sept. 20, 2022. (AP Photo/Andrew Harnik, File)

Sullivan said Biden administration officials believe there are a number of options that "could potentially lead to a positive result here."

Sullivan explained that "the big challenge" the administration has had over the past several months with regard to Whelan’s release is that Russia had been asking for something that officials have not been able to give, but he maintained that the challenge is one that the Biden administration is "up to."

"That is a problem we are trying to solve," he said. "I will just reinforce that our commitment to this is absolutely rock solid, intense."

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"This is as high a priority as the president has," he said.

Sullivan’s comments come after the Biden administration successfully brokered the release of WNBA player Brittney Griner last week. Griner was turned over in exchange for the release of convicted Russian arms dealer Viktor Bout, who was once nicknamed "the Merchant of Death."

Brittney Griner Russia Viktor Bout

Brittney Griner is escorted from a courtroom after a hearing in Khimki, just outside Moscow, Russia, Aug. 4, 2022. (AP Photo/Alexander Zemlianichenko, File)

The president and administration officials have stressed that the United States did not have "a choice of which American to take home," and Biden maintained that Russia is treating Whelan differently "for totally illegitimate reasons."

"We will never give up," Biden said last week.

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On Monday, Sullivan maintained that the Biden administration is working to "come up with the right formula" to be able to present to the Russian Federation to secure Whelan’s release.

"We’re determined to figure out how to do that. That is what we’re working on," he said.