The top Democrat on the House Intelligence Committee on Thursday accused FBI Director James Comey of withholding information from key lawmakers in Congress about a probe of Russia interference in the 2016 elections, as lawmakers charged that top leaders in Congress were seemingly kept out of the loop on the details of the politically charged investigation.

"In order for us to do our investigation in a thorough and credible way, we're going to need the FBI to fully cooperate," Rep. Adam Schiff said after an over three hour closed door briefing with the FBI Director.

"He made it very clear there were certain questions that we were asking that he would answer, and others that he would not," said Schiff.

"At this point we know less than a fraction of what the FBI knows," Schiff told reporters.

With the Chairman of the Intelligence Committee, Rep. Devin Nunes (R-CA), standing nearby and listening, Schiff gave one answer that raised major red flags, saying that the FBI had not divulged information about Russia-related investigations to what is known as the "Gang of Eight."

The Gang of Eight is the group of lawmakers made up of the top member of each party on the House and Senate Intelligence committees, plus the top leaders of each party - sometimes an administration will share secret matters just with those members, in order to prevent leaks.

"I think the Chair and I are in agreement on this - these are issues that should have been brought to the Gang of Eight, at a minimum," Schiff said, who said lawmakers had not been given important information in quarterly briefings over the past year.

"So to be clear, you learned things today that you had not previously been aware of as a member of the Gang of Eight?" a reporter asked.

"Absolutely," said Schiff, who refused to go into any detail. "I'm going to leave it at that."

It was not clear what information had been withheld - and only briefed to lawmakers on Thursday - as it was the second somewhat puzzling visit to Capitol Hill by Director Comey in the last three weeks.

The first - a briefing for the Senate Intelligence Committee in mid-February - was remarkable for the lack of comment by members of the panel after the meeting was over.

This time - the news signaled that lawmakers were only learning about some facets of the Russia probe for the first time, with fingers being pointed directly at the FBI.