Updated

Republican lawmakers are stepping up their campaign to gain access to the survivors of the Benghazi terror attack, with one claiming the Obama administration is engaging in a "cover-up" and another threatening to bring "legal charges."

The frustration is mounting six months after the Sept. 11 attack on a U.S. consulate in Libya. Republicans have sparred with the Obama administration over a range of issues -- from the faulty explanation over what caused the attack to the warning signs missed in advance of it -- but have focused recently on the surviving victims. They say they've been stonewalled in their attempts to get a list of survivors and speak with them.

Rep. Frank Wolf, R-Va., told Fox News on Tuesday that some have been at a Washington-area military hospital since the attack, saying their injuries must be "serious."

Yet, he said, "we don't honor these people, we don't mention their names."

"It's like it's a dark hole, and I think we're now at a point -- now there is a cover-up," Wolf told Fox News, calling for a "select committee" to investigate Benghazi.

On Monday, Rep. Dana Rohrabacher, R-Calif., also sent a letter to Secretary of State John Kerry, complaining that the department "appears to be stonewalling a legitimate request for information, perhaps as part of an effort to cover up evidence of wrongdoing or incompetence."

He wrote that the House Foreign Affairs Committee, on which he sits, has the right to know "what the survivors saw and experienced ... on that dreadful night."

The congressman said he would recommend to top Republican lawmakers that "legal charges" be brought if the situation does not "immediately improve." It's not clear who those charges might be leveled against, but it was an apparent reference to lawmakers' ability to bring contempt of Congress claims.

Estimates of how many Americans were injured in the Libya assault vary. Wolf, R-Va., and Jim Gerlach, R-Pa., have claimed sources told them up to 30 were injured, and up to seven may still be at the Walter Reed military hospital.

A source close to the survivors, though, told Fox News that seven were injured -- not 30 -- and that at least three are still at Walter Reed.

Fox News has been told that some of the survivors work in clandestine services and do not want their names made public.

The State Department has declined to say how many survivors were injured or hospitalized.

Secretary of State John Kerry, in an interview with Fox News, revealed last week that he has visited one of the survivors in Bethesda, Md. -- the location of Walter Reed.

Kerry described the survivor as "remarkably courageous" and doing "very, very well." He also said he also talked to the unnamed survivor's wife.

Asked when the public might hear from the survivors, Kerry said "I can't tell you -- I don't know what the circumstances are of any requests to talk to them or not."

Senate Republicans are also expected to press Kerry on making the surviving victims available.

Meanwhile, House Intelligence Committee Chairman Mike Rogers, R-Mich., told Fox News on Monday that he thinks the ongoing FBI probe is going too slow because foreign governments have blocked direct U.S. access to suspects -- and because of a failure by the U.S. government to provide "appropriate" resources.