The chairman of the U.S. Senate Intelligence Committee said on Tuesday he plans to hold public hearings on possible links between President Donald Trump's campaign and Russia, although he did not say when they would take place.

"It will happen," Republican Senator Richard Burr told reporters after a closed committee meeting. Asked if he knew when, he said, "I don't yet, but soon."

The House of Representatives Intelligence Committee, which, like the Senate panel, is conducting its own investigation of the possible Russia ties, will hold its first public hearing on Monday.

Congressional Democrats have called for a special prosecutor or non-partisan select committee to investigate the matter. But Trump's fellow Republicans, who control majorities in both the Senate and House, say the various probes by congressional committees are sufficient.

U.S. intelligence agencies said in January that Russia had conducted cyber attacks on Democrats in an effort to influence the 2016 U.S. election on Trump's behalf. Russia has denied this.

Burr also said he did not now plan to follow the lead of other congressional committees that have requested any warrant applications or court documents related to Trump's assertion that former President Barack Obama had wiretapped Trump Tower.

Trump gave no evidence to support his charge, which former Obama administration officials have denied.

When asked to explain why he had not asked for such evidence, Burr said he felt it was unnecessary.

"We've had sufficient conversations and gotten answers that we find to be satisfactory from the appropriate folks," Burr said, when asked to explain why he would not request.

The leaders of the House of Representatives Intelligence Committee and the Senate Judiciary Committee's Subcommittee on Crime and Terrorism have requested evidence about the alleged wiretapping. The Justice Department has asked for more time to respond.

Democratic Senator Joe Manchin, a member of the Senate Intelligence Committee, told reporters after leaving the closed committee meeting on Tuesday that he had still not seen any evidence to back up Trump's wiretapping claim.

Burr declined comment on whether he had seen any evidence.