The Russian lawyer at the heart of the scandal over a meeting with US president Donald Trump's eldest son claimed on Wednesday she was ready to testify to congress.
Lawyer Natalia Veselnitskaya attended a meeting with Donald Trump Jr during the presidential election campaign in June last year at which it appears he expected to get incriminating information from the Russian government on his father's rival, Hillary Clinton.
Mr Trump Jr had been told by e-mail that a "Russian government attorney" would provide damaging details. Trump campaign manager Paul Manafort and the president's son-in-law Jared Kushner also attended.
Ms Veselnitskaya has rejected claims that she was working on behalf of the Russian government, while Mr Trump Jr insists that no sensitive information was passed on.
In an interview with the Kremlin-controlled RT television channel, Ms Veselnitskaya said she was "ready" to speak to the US congress about the meeting "if my security can be assured".
The firestorm around the meeting is the latest chapter in the scandal over possible ties between the Trump campaign and Moscow.
US intelligence agencies have accused Russian president Vladimir Putin of approving a hacking and influence campaign to sway last year's presidential election - allegations rejected by the Kremlin.
The Trump administration is currently under investigation by both the US congress and the FBI over any possible collusion.
Ms Veselnitskaya's remarks came a day after the White House acknowledged that Mr Trump and Mr Putin had an additional, previously undisclosed conversation at the G20 summit in Hamburg earlier this month.
After a brief greeting at the start of the two-day summit and a two-hour bilateral meeting with their foreign ministers on July 7, the two leaders also chatted over dinner on the final night of the summit, an official said on Tuesday.
"There was a couples-only social dinner at the G20," the official said. "Toward the end, the president spoke to Putin at the dinner."
White House spokesman Sean Spicer and National Security Council spokesman Michael Anton later confirmed the conversation had taken place.
Mr Anton would not specify the duration of the discussion, but said it was casual and should not be characterised as a "meeting" or even a less formal, but official, "pull-aside".
The disclosure has raised questions about what the pair talked about, who was present and why the meeting was not previously mentioned.
The US president defended the G20 dinner in a pair of angry tweets late on Tuesday, saying it had been on his public schedule.
"Fake News story of secret dinner with Putin is "sick." All G 20 leaders, and spouses, were invited by the Chancellor of Germany. Press knew!," he wrote.
"The Fake News is becoming more and more dishonest! Even a dinner arranged for top 20 leaders in Germany is made to look sinister!"
The White House also rejected concerns that Mr Trump was not with any other US officials and used Mr Putin's translator.
"Each couple was allowed one translator. The American translator accompanying president Trump spoke Japanese," a second White House official said. "When president Trump spoke to president Putin, the two leaders used the Russian translator, since the American translator did not speak Russian."
A senior Russian lawmaker meanwhile dismissed media reports of an undisclosed conversation between Mr Trump and Mr Putin as sensationalist.
Alexei Pushkov, chairman of the information policy at the upper house of Russian parliament, lashed out at US media for seeking details of "a secret conversation that didn't happen".
"They're sick," he added.
* Additional reporting by Associated Press