A former foreign policy adviser to US president Donald Trump has branded a congressional probe into possible interference by Russia in last year's American election "a comically fake inquiry".
However, Carter Page (pictured) pledged to co-operate with the investigation, which has asked several of Mr Trump's associates to turn over information about possible contacts with Russian officials or businessmen.
Former National Security Adviser Michael Flynn, Republican strategist Roger Stone and former Trump campaign chairman Paul Manafort are also among those the Senate intelligence committee has asked to provide information and documents related to its investigation.
Both the Senate and House intelligence panels along with US intelligence and law enforcement officials are investigating Russian efforts to influence the 2016 presidential election.
FBI director James Comey said the FBI probe is exploring the nature of any links between individuals associated with Mr Trump's campaign and the Russian government, and whether there was any co-ordination between Russia's efforts and that campaign.
The Senate committee would not disclose which individuals it is targeting, but Mr Stone said he intended to comply with the committee's requests.
"I am eager, indeed anxious, to testify in full public session, have requested no immunity and am ready to go," Mr Stone wrote.
He also said that he "rejects" the claim that WikiLeaks founder Julian Assange and Guccifer 2.0, the unnamed hacker that has taken credit for breaking into the Democratic National Committee servers, are Russian assets.
He said the US government has offered no proof to support that assessment.
Mr Stone communicated through Twitter direct messages with Guccifer 2.0. Mr Stone has said that he was unaware at the time that US officials believed the hacker had ties to Russia.
The letters the committee sent to Mr Stone and Mr Page, which have been obtained by reporters, were virtually identical. The committee asked them to provide emails, text messages, letters, phone records or any other relevant information they have about meetings or contacts that they or any other individual affiliated with the Trump campaign had with Russian officials or representatives of Russian business interests.
The requests seek information about any contacts that occurred between the day Mr Trump announced his candidacy, June 16 2015, and his inauguration on January 20 this year.
It also asks for information about Mr Stone and Mr Page's financial and real estate holdings related to Russia, including financial securities or holdings they might have sold or divested during that period.
In a written response to the committee's request, Mr Page argued that the panel was conducting a "comically fake inquiry". At the same time, he pledged to co-operate with the committee to "help resolve all of the false allegations which led to this fanciful witch hunt in the first place".
The committee also asks that Page and Stone appear for closed interviews with intelligence committee staff, with a May 9 and May 19 deadline for various materials to be provided to the probe.