The top Democrat on the House Intelligence Committee said FBI Director James Comey is not providing lawmakers trying to probe Russian interference in U.S. affairs enough information to do their job.

"In order for us to do our investigation in a fair and thorough way, we're going to need the full cooperation of the FBI," Rep. Adam Schiff, D-Calif., said Thursday. "At this point the director was not willing do that," he said after Comey briefed committee members.

Comey wouldn't answer lawmakers' questions about what the full scope of their investigation into matters involving Moscow is, Schiff said.

"It is unclear if that was a decision he was making on his own or a decision he was making in consultation with the Department of Justice," Schiff said. "That cannot persist. If we are going to do our jobs, the FBI has to fully cooperate with us. And that means that the FBI can't say, 'we will tell you this but we won't tell you about that.'"

Schiff said that the FBI still hasn't fully briefed the "Gang of 8"—House and Senate leaders who receive the most sensitive national security information—about what Russia may or may not have done in terms of hacking Democratic officials' emails, attempting to influence the presidential election, or initiating contact with Trump campaign or administration officials.

"I'm disappointed we didn't have that briefing today," Schiff said.

"We hope we get a different answer from the director the next time we meet," he added. "We know less than a fraction of what the FBI knows."