The State Department said Wednesday that officials are prepared to meet immediately with a special House committee investigating the deadly 2012 attacks in Benghazi, Libya.

In a letter to the panel's Republican chairman and top Democrat, Assistant Secretary of State Julia Frifield said officials could meet "as soon as today" to schedule interviews with up to 22 potential witnesses who work for the State Department or have knowledge of the attacks.

Since many of the potential witnesses work overseas, "we will need flexibility as to which precise order they appear...but can commit to dates," Frifield wrote in the letter, a copy of which was obtained by The Associated Press.

The letter comes a day after Rep. Trey Gowdy, R-S.C., the chairman of the Benghazi panel, complained about resistance from the State Department and vowed to "ratchet up" his inquiry.

"Letters haven't worked. Southern politeness hasn't worked. We're going to ratchet it up," Gowdy said at the end of a two-hour hearing Tuesday.

Officials from the Justice Department and Central Intelligence Agency have been more cooperative, Gowdy said, reserving his ire for the State Department.

The 12-member panel was created last May to investigate the September 2012 attacks on a U.S. post in eastern Libya that killed U.S. Ambassador Chris Stevens and three other Americans.

Gowdy told reporters after Tuesday's hearing that he is likely to call former Secretary of State Hillary Rodham Clinton as a witness, but not until he receives more emails and other documents from the State Department.

"What I am not going to do is ask my colleagues to question (Clinton) when they don't have all of the relevant documents and emails. We don't have the emails," Gowdy said, adding that it is up to the State Department and committee Democrats how quickly Clinton's testimony can be scheduled.

Rep. Elijah Cummings of Maryland, the panel's senior Democrat, said Clinton stands ready to testify if called. Cummings said he spoke to Clinton late last year and she "immediately" agreed to testify.

"If the committee wants her to come, she's willing to come," he said.

Cummings has complained that the committee's investigation is moving at a "glacial" pace and said he and other Democrats "have grave concerns about the partisan path this committee has taken over the past year."