A former Soviet counter-intelligence official attended a meeting last year with senior aides to President Donald Trump and his son, it has emerged, BBC report.
Rinat Akhmetshin, now a lobbyist, confirmed to US media he was present at the Trump Tower encounter.
Donald Trump Jr was promised damaging material on Hillary Clinton at the meeting, his emails show.
Mr Trump Jr has only previously acknowledged that a Russian lawyer, Natalia Veselnitskaya, was present.
The president’s eldest son has played down the 9 June 2016 meeting since it was reported this week.
But the Senate Judiciary Committee has asked 39-year-old Mr Trump Jr to publicly testify.
Several congressional panels and federal investigators are looking into claims that Russia meddled in last year’s US election in a bid to help Donald Trump.
The New York meeting was also attended by the president’s son-in-law, Jared Kushner, and election chairman, Paul Manafort.
It has emerged as the firmest evidence yet of non-diplomatic interactions between Trump campaign aides and Russian figures.
During a news conference in Paris, France, on Thursday, Mr Trump said that “most people would have taken that meeting”.
“Zero happened,” the president said.
Who is Rinat Akhmetshin?
Mr Akhmetshin told the AP news agency he served in a Soviet military unit that was part of counterintelligence, but that he was never formally trained as a spy.
In court papers filed in 2015 with the US District Court in Washington DC, where he lives, a mining company accused him of organising a hack on its private records as part of an alleged smear campaign.
International Mineral Resources hired a private investigator to follow Mr Akhmetshin to London.
The Russian-American was overheard in a coffee shop bragging about arranging the cyber-attack on the firm’s computer system, according to court documents.
Mr Akhmetshin denied the allegations, and the case was later dropped.
Kremlin spokesman Dmitry Peskov says the Russian government knows nothing about Mr Akhmetshin, the AP reported.
Mr Akhmetshin told the Washington Post he became a US citizen in 2009 but retains his Russian nationality.
He is a registered lobbyist who has focused in recent years on overturning the 2012 US Magnitsky Act.
The law, which froze the assets of senior Russian officials, angered President Vladimir Putin.