First on CNN: Former Gov. Bill Richardson held meetings in Moscow this week with the Russian leader

Details of those meetings were not immediately clear. Richardson, a former New Mexico governor and diplomat, and his eponymous center work privately on behalf of the families of hostages and detainees, and the trip Biden administration works to free two Americans wrongfully detained by the State Department: Brittney Griner. and Paul Whelan.

A spokeswoman for the Richardson Center told CNN on Tuesday that “we cannot comment on this at this time.”

CNN has reached out to the State Department, the National Security Council, and Reps. Griner and Whelan.

Richardson has long worked to secure the release of Americans detained overseas, and in April played a role in securing the release of Trevor Reed from Russian custody.

A source familiar with the situation told CNN in April, after Reed’s release, that members of the Richardson Center traveled to Moscow in February, in the days leading up to the start of Russia’s war in Ukraine, to meet with Russian leadership. After that visit, the Richardson Center came away with a clear sense of what the Russians were willing to do and how they were willing to do it, which was presented to the White House.

The Biden administration has repeatedly said that working to secure the freedom of Griner and Whelan, as well as other Americans wrongfully detained abroad, is a top priority.

In late July, US Secretary of State Antony Blinken announced that the US had made a “substantial proposal” to try to secure the release of Griner and Whelan. Sources told CNN the proposal included a swap for convicted arms dealer Viktor Bout.

Last week, State Department Deputy Spokesman Vedant Patel said that “the US government continues to urge Russia to release the wrongfully detained individuals Brittney Griner and Paul Whelan.”

“As you all know, the Secretary came and spoke to you a few weeks ago, where he made it clear that there was a significant proposal on the table last week to facilitate their release, and our governments have repeatedly and directly communicated about that proposal,” he said.