In addition to those four subpoenas, the committee has issued three others - to the National Security Agency, the Federal Bureau of Investigation and the CIA - for information about requests that government officials made to "unmask" the identities of US individuals named in classified intelligence reports, according to a congressional aide.
Michael Flynn, President Trump's short-tenured national security adviser, has taken the Fifth to avoid handing over personal documents subpoenaed by the Senate Intelligence Committee, but he has reportedly agreed to turn over some business records demanded by the Senate panel investigating Russia's machinations in the 2016 presidential race.
One of President Donald Trump's personal attorneys, Michael Cohen, has received an "invitation to provide information and testimony" that pertains to the Russian Federation investigation to House and Senate intelligence committees, Cohen has confirmed.
The subpoenas are part of an effort by congressional investigators to obtain testimony, personal documents and business records from Michael Cohen, Michael Flynn, and their business firms. "We will continue to pursue this investigation wherever the facts may lead".
But a senior committee aide said he could not confirm that those subpoenas had been issued, and he added that if they had been, it was not with the agreement of the Democratic members of the panel or as part of the committee's Russian Federation probe.
At the White House on Wednesday, spokesman Sean Spicer told reporters that he would no longer answer questions about Comey or the Russian Federation investigation. The aide declined to be identified because he was not authorized to discuss committee activities publicly.
While the Senate committee awaits documents from Flynn, Putin and Trump both dismissed the US intelligence community's conclusion that the Kremlin interfered in the 2016 USA presidential election by hacking Democratic emails. Richard Burr, the North Carolina Republican who chairs the committee, says the committee would welcome Comey's testimony.
Congress is due back in session next week.
A spokeswoman for the committee's chairman, Sen.
The Associated Press reported earlier this month that Comey planned to testify before the Senate committee after Memorial Day, but the approval from Mueller to do so could indicate that date is fast approaching.
The latest committee action shows that lawmakers have not given up their own Russian Federation investigations despite a separate FBI probe led by former FBI director Robert Mueller, who was appointed as special counsel by Deputy Attorney Rod Rosenstein on May 17.
Flynn's decision Tuesday came as President Donald Trump's personal attorney, Michael Cohen, rejected a House intelligence committee request for information.
The subpoena for Cohen comes as the congressional investigations into ties between the Trump campaign and Russian Federation advance beyond formal requests for information from Trump associates.
The subpoenas asked the spy agencies to provide details of any requests made by two top Obama administration aides and the former CIA director to "unmask" names of Trump campaign advisers inadvertently picked up in top-secret foreign communications intercepts, congressional sources said.
- By Jake Pearson in NY.