Bill Richardson, former US ambassador to the UN and a frequent hostage negotiator who has worked on the cases of American detainees Brittney Griner and Paul Whelan, visited Moscow this week, US media outlets have said.
The reported visit comes as US officials continue to push for the release of Griner, the basketball star who was sentenced last month to nine years in prison on a drug possession conviction. Griner has been detained in Russia for more than 200 days since being arrested at a Moscow airport in February.
The US has also pressed for the release of Paul Whelan, a former US Marine serving a 16-year sentence on espionage charges.
Washington has classified both Americans as wrongfully detained by Russia.
Secretary of State Antony Blinken said in July that the US made a “substantial proposal” to Russia to facilitate a prisoner exchange. As part of that deal, Washington reportedly would release convicted arms trader Viktor Bout.
Mr Richardson expressed hope for a two-for-two swap in an interview with the Associated Press last month.
The Kremlin on Wednesday said it had no comment on Mr Richardson's reported visit.
“There were no meetings at the Kremlin,” spokesman Dmitry Peskov told reporters on a conference call. “I have nothing to tell you on this subject.”
Moscow last month said it was engaged in “quiet diplomacy” with Washington about a potential prisoner swap.
CNN first reported on Tuesday that Mr Richardson, who also previously served as governor to the US state of New Mexico, travelled to Moscow to hold talks with Russian officials.
Agencies contributed to this report
