U.S. President Donald Trump sought to insert himself into congressional investigations on Russia on Wednesday, urging lawmakers to hear from one of his former advisers, Carter Page, to counter testimony by directors of the FBI and CIA.

Trump has been dismissive of probes by the FBI and several congressional panels into alleged Russian meddling in the 2016 presidential election and potential collusion with his campaign.

In a series of early morning tweets, the Republican president quoted a Monday letter from Page in which he asked to address the House Intelligence Committee promptly and referred to faulty testimony from U.S. intelligence officials.

Trump accused Democrats of blocking Page's testimony, without citing evidence but referring to an unidentified report.

"So now it is reported that the Democrats, who have excoriated Carter Page about Russia, don't want him to testify. He blows away their case against him & now wants to clear his name by showing 'the false or misleading testimony by James Comey, John Brennan...' Witch Hunt!" Trump wrote on Twitter, referring to the former directors of the FBI and CIA.

Trump's tweets came as his advisers are planning to establish a "war room" to combat mounting questions about communication between Russia and his presidential campaign before and after November's election.

The White House said on Wednesday it would not answer any more questions about the investigations.

"Going forward all questions on these matters will be referred to outside counsel Marc Kasowitz," White House spokesman Sean Spicer told reporters when asked about a media report on what Comey planned to say in congressional testimony.

White House spokesman Michael Short confirmed that the new policy would apply to all aspects of the Russia probes being conducted by Congress and the Federal Bureau of Investigation.

However, the president's penchant for tweeting could complicate White House efforts to tamp down the scandal if the messages appear to address the investigations.

Representative Adam Schiff, the top Democrat on the House Intelligence Committee, swatted back at Trump on Twitter with a reference to the president's acknowledgment to NBC that he was thinking of "this Russia thing" when he fired Comey on May 9.

"@POTUS, appreciate suggestion on witnesses but feel you may not have probe's interests at heart. Ex: Firing FBI Dir because of Russia probe," Schiff wrote.

Democrats say Comey's dismissal was aimed at hindering the FBI's Russia investigation, which has since been taken over by a special counsel, Robert Mueller, himself a former FBI director.

'STOP TWEETING ABOUT IT'

Trump's fellow Republicans, including Senate Majority Leader Mitch McConnell, have urged him to tweet less and more wisely. U.S. Representative Sean Duffy said on Wednesday the Russia investigations were becoming too much of a distraction in Trump's 4-month-old presidency.

"I think the president should step aside from any comments, any tweets on the investigation and focus on the agenda that he ran on," Duffy said on CNN. "Stop tweeting about it, stop talking about it and get about the business of your agenda."

Page, who provided a copy of his letter to Reuters, said the committee postponed an appearance scheduled for next week without giving a specific reason.

Schiff said he and the Republican overseeing the committee's probe, Representative Mike Conaway, want to review documents before interviewing witnesses.

"While we anticipate interviews to begin shortly, we have agreed that the pace of those interviews will be dictated by the needs of the investigation and not the preferences of outside parties," he said in a statement.

Republicans control both the House of Representatives and the Senate.

Page, a businessman who worked in Russia at U.S. investment bank Merrill Lynch, advised Trump during his presidential campaign.

Russia has denied U.S. intelligence agencies' conclusion that Moscow interfered in the election campaign to try to tilt the vote in Trump's favor. The president has denied any collusion.

Congressional committees have contacted a parade of Trump associates and advisers, as well as former White House officials, to request information in their probes.

They include former White House national security adviser Michael Flynn, Trump, former campaign manager Paul Manafort, former White House press officer Boris Epshteyn, personal lawyer Michael Cohen and informal adviser Roger Stone.