MOSCOW (Reuters) - Saudi Crown Prince Mohammed bin Salman and Russia's sovereign wealth fund chief Kirill Dmitriev were involved in negotiations over the release of U.S. teacher Marc Fogel from a Russian prison, a source close to the negotiations between Russia and the United States told Reuters on condition of anonymity.

The Kremlin could not be reached for immediate comment. The Saudi embassy in Moscow did not immediately reply to a request for comment. Saudi Crown Prince, also known as MbS, helped to negotiate the prisoner swap in August 2024.

U.S. President Donald Trump's Middle East envoy, Steve Witkoff, took Fogel back to the United States from Moscow on Tuesday after an unannounced stop in Russia.

Witkoff was quoted by a CNN reporter on X as saying that MbS was "instrumental as well" and that "a gentleman from Russia" by the name Kirill "had a lot to do with this".

Russian President Vladimir Putin, who visited Saudi Arabia in 2023, said last September that he was grateful to Mohammed bin Salman for his role in the previous exchange.

Putin and Mohammed bin Salman have fostered a close personal relationship since 2015 when the prince visited Russia for the first time. Reuters reported this month that Saudi Arabia seen by Russia as possible venues for a Russia-U.S. summit.

Dmitriev, a U.S.-educated former Goldman Sachs banker, played a role in early contacts between Moscow and Trump's team when he was first elected President in 2016.

Dmitriev earlier played a role in releasing U.S. investment banker Michael Calvey from Russian prison in 2019. He called Calvey a professional investor and personally vouched for him.

(Reporting by Moscow Newsroom; editing by Guy Faulconbridge)