The top Democrat on the House Intelligence Committee on Thursday accused FBI Director James Comey of withholding crucial information about its probe into Russian interference in the election, and raised the prospect of subpoeaning the agency.

"I would say at this point we know less than a fraction of what the FBI knows,” Rep. Adam Schiff (D-Calif.) told reporters after a briefing with Comey.

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“I appreciate we had a long briefing and testimony from the director today, but in order for us to do our investigation in a thorough and credible way, we're gonna need the FBI to fully cooperate, to be willing to tell us the length and breadth of any counterintelligence investigations they are conducting,” Schiff said. “At this point, the director was not willing to do that.”

The briefing came as Attorney General Jeff Sessions is facing calls to recuse himself from an investigation into ties between the Trump campaign and Russia after The Washington Post reported that Sessions met twice with the Russina ambassador last year, and didn’t tell senators about it during his confirmation hearing.

During the briefing, Schiff said, Comey faced “repeated questions about the scope of any investigation they were doing” and “individuals that may be the subject of any counterterrorism investigation.”

“The director declined to answer those questions,” Schiff said.

Schiff also raised the prospect that it could have been Sessions' Justice Department that advised Comey to be less than forthcoming. “It was unclear whether that decision was a decision he was making on his own or a decision that he is making in consultation with the Department of Justice," he said.

Schiff added that lawmakers have yet to be fully briefed on counterintelligence by the FBI. “That can’t persist,” he said. “If we’re gonna do our job, the FBI is going to have to fully cooperate with us, and that means they can't say, ‘We’ll tell you about this, but we won't tell you about that.’”

The House intel ranking member also indicated that Comey and the Justice Department should be more cooperative and forthcoming at their next meeting “because we’re gonna need that information.”

“And we’re better off getting that through the voluntary cooperation of the FBI than having to contemplate whether we need to subpoena the FBI,” he warned.

The embattled attorney general has faced a growing number of calls from fellow Republicans urging him to recuse himself from any investigation into Trump’s ties to Russia, while Democratic leaders have insisted that Sessions resign from his post as the nation’s chief law enforcement official.

“Up until now, I wasn’t sure whether there should be a special prosecutor because that is a function of a couple of things. It’s a function of whether the attorney general can be independent or whether there’s a conflict of interest or an appearance of impropriety — and whether there’s something concrete and specific enough to be investigated,” he said. “I am now convinced that both of those criteria are met and that an independent prosecutor should be appointed. Certainly, the attorney general is in no position to oversee any investigation or prosecution involving any of the counterintelligence issues concerning Russia. So I am now convinced that an independent prosecutor is necessary.”