U.S. Democrats are charging that FBI Director James Comey declined to divulge all he knew about the agency's investigation into Russian meddling in the U.S. election at a closed-door meeting with the House Intelligence Committee.

"At this point, we know less than a fraction of what the FBI knows," said Representative Adam Schiff, the committee's top Democrat, after Comey's three-hour briefing on March 2.

The committee, like the FBI, is investigating allegations of collusion between Russia and President Donald Trump's campaign last year.

"There were very large areas that were walled off, and those walls are going to have to come down if we are going to do our job,” Schiff said

"It was unclear whether [Comey's refusal to discuss certain matters] was a decision he was making on his own or a decision that he is making in consultation with the Department of Justice," Schiff said.

The committee's Republican Chairman Devin Nunes dismissed the Democratic complaints, saying Comey was "forthright" and that the briefing was a "good first step."

U.S. intelligence analysts have concluded that Russia tried to help Trump win the White House by discrediting Democratic presidential nominee Hillary Clinton through the release of hacked party e-mails.

Based on reporting by AP and Reuters