US Secretary of State Antony Blinken spoke by phone on Wednesday with American citizen Paul Whelan, who is being held in a Russian prison, a source said.
Mr Blinken told Mr Whelan to “keep the faith and we’re doing everything we can to bring you home as soon as possible", CNN reported.
Mr Whelan, a former US Marine, was arrested in 2018, held for 18 months in Lefortovo prison in Moscow and jailed for 16 years in 2020 on spying charges. He has denied the accusations.
Russian ambassador to the US Anatoly Antonov said Moscow and Washington are using an effective channel to swap prisoners.
Also jailed in Russia is The Wall Street Journal reporter Evan Gershkovich.
“The issue of prisoner swaps is solved by authorised bodies which presidents agreed about in 2021,” Mr Antonov said on his official Telegram channel. “The special channel proved to be effective."
He was referring to the prisoner swaps of Russian arms dealer Viktor Bout and Russian pilot Konstantin Yaroshenko for US basketball star Brittney Griner and former US marine Trevor Reed last year.
The US has designated Mr Whelan as “wrongfully detained", a term that effectively says the charges are bogus and the case is politically driven.
US ambassador to Russia, Lynne Tracy, visited Mr Whelan in May in the prison in eastern Russia where he was being held.