Graham told reporters on Wednesday that he was in the dark, beyond press reporting, about what was driving the administration's actions on Iran and that he intended to request a briefing.

"Removing personnel from within the embassies and the consults is clearly a serious move by the State Department. They feel the threat, and I would urge the State Department and DoD [Department of Defense] to come down here and explain to us what's going on," Graham told reporters.

He added that he has "no idea what the threat stream is beyond what I read in the paper, and I think there are a lot of people in my shoes that are going to support standing up to Iran but we need to understand what we're doing."

Graham told reporters on Thursday that he hadn't gotten an update from the administration but that he and Leahy had sent the letter formally requesting the briefing.

The administration on Thursday afternoon is scheduled to brief the Gang of Eight, which is comprised of the leaders of both parties in each chamber of Congress as well as the chairmen and ranking members of the House and Senate intelligence committees.

Senate Minority Leader(D-N.Y.) has also called for acting Defense Secretaryand Chairman of the Joint Chiefs Gen. Joseph Dunford to testify publicly before the Senate Armed Services Committee.