WASHINGTON -- A longtime adviser to President Donald Trump says he has been asked by the Senate intelligence committee to retain any documents that could be related to its investigation into Russia’s interference in the 2016 election.

Roger Stone says he welcomes the opportunity to publicly testify before lawmakers. Stone says neither he nor Trump “have anything to fear in a fair, balanced inquiry.”

The Senate and House intelligence committees are investigating Russia’s hacking of Democratic groups and possible contacts between Trump associates and Russia.

Stone has said he communicated with the hacker, Guccifer 2.0, who has taken credit for breaching the Democratic National Committee. Stone called the contacts “innocuous.”

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“There’s no collusion here,” Roger Stone told CBS News correspondent Jeff Pegues last week, while he admitted to contact with Guccifer 2.0, the Twitter handle that released hacked election information believed stolen from Democratic Party servers.

He called the contact an “exchange,” which appears to have started after Guccifer’s first Twitter account was suspended and then re-activated in mid-August.

Earlier this year, U.S. intelligence concluded that the Guccifer sites were a front for Russian military intelligence; Stone says he had no idea, Pegues reported.

On at least 16 different occasions during the 2016 campaign, Guccifer disclosed Democratic Party data targeting Hillary Clinton and Democratic candidates in at least six different states.

Carter Page, who briefly served as a foreign policy adviser to Trump’s campaign, has also said he was contacted by the Senate panel about its investigation.