WASHINGTON (AP) — A leading Republican senator is threatening to hold up Senate confirmation of President Barack Obama’s nominees to lead the Defense Department and the CIA until the White House provides more answers about the deadly Sept. 11 attack against a U.S. diplomatic facility in Benghazi, Libya.

Sen. Lindsey Graham is angered by what he calls White House “stonewalling” about the attack that killed four Americans, including the ambassador.

Graham tells CBS he’ll hold up Senate action on the nominations of Chuck Hagel as defense secretary and John Brennan as CIA director until he gets what he wants.

The senator wants to know what Obama was doing during the time of the attack and whether he was in touch with Libyan officials.

Democratic Sen. Jack Reed calls Graham’s threat “unprecedented and unwarranted.”