Updated

Republican Sen. Lindsey Graham says he will block Chuck Hagel’s confirmation process for secretary of defense until outgoing Secretary Leon Panetta testifies about the fatal attacks on U.S. facilities in Benghazi, Libya.

Graham has been among the most vocal and persistent Republican lawmakers in calling for answers about the Sept. 11, 2012, attacks on a U.S. outpost that killed four Americans, including a U.S. ambassador.

“I'm going to block Hagel from going forward until (Panetta) does,” the South Carolina senator said Monday night on Fox News’ “On the Record with Greta Van Susteren.” “Why would we not want to understand what happened during the attack?”

Hagel’s nomination process is scheduled to begin Thursday.

Pentagon spokesman George Little said Tuesday that Panetta would respond to the request but he didn’t know whether Panetta would agree to testify.

However, Little said keeping the confirmation process moving forward is “very important,” that the Pentagon has been forthcoming with Congress on the U.S. military response to the Benghazi incident and that Hagel would do an “outstanding” job.

Hagel, a former Nebraska Republican senator, was nominated by President Obama and is expected to face tough questions during the Senate confirmation hearings about his support for Jerusalem and whether he would back military action should the nuclear threat from Iran escalate.

Graham and other Republican lawmakers continue to seek answers about the incident -- after already seeing a State Department report on the attack, questioning Secretary of State Hillary Clinton for roughly 10 hours during open Capitol Hill testimony and grilling U.S. Ambassador Susan Rice, whose less-than-exact explanation of events essentially cost her the secretary of state nomination.

Graham and other senators have said their decision on Hagel will depend on what he says during the hearings in the Democrat-controlled Senate, “but the one thing I'm not going to do is vote on a new secretary of defense until the old secretary of defense, Leon Panetta, whom I like very much, testifies.”o

Among Graham’s lingering questions are what happened during the seven-hour attack on the Benghazi outpost and what was Obama’s response, including whether he gave orders to send in help.