The U.S. has been denied direct access to the only publicly known suspect in custody in connection with the Benghazi terror attack, Fox News has learned, with U.S. interrogators still unable to sit in the same room as the Egypt-held prisoner to ask questions.

Abu Ahmed, also known as Mohammed Jamal, is suspected of establishing Islamist training camps in Eastern Libya where militants who took part in the Sept. 11 Benghazi terrorist attack were able to train.

Ahmed is not suspected of directly taking part in the attack which left four Americans, including Ambassador Chris Stevens, dead. But this is at least the second time U.S. interrogators have been denied access to a suspect held by a foreign government.

In January, Tunisian authorities released Ali Ani al-Harzi, who is suspected of taking part in the attack, citing a lack of evidence.

FBI agents finally got access to al-Harzi after the personal intervention of Republican Sen. Lindsey Graham.

Thomas Joscelyn, with the Foundation for Defense of Democracies, said some of the militants Ahmed helped train "directly took part" in the Benghazi attack.

"As early as 2011, he was setting up training camps inside eastern Libya as early as 2011 ... and they were drawing in recruits from around North Africa and Egypt -- if you bring them in, train them in terms of how to operate mortars and various types of heavy artillery, and it's that type of artillery that was used in the attack in Benghazi."

Joscelyn, who was the first to report the access problem, said he's been told U.S. officials have asked the Egyptians for access to the suspect but were denied by the Egyptian authorities.

"The Egyptians like to control the interrogations and interviews of these suspects for their own reasons and of course the Americans should want access for our purposes as well," he said.

Neither the CIA nor FBI provided comment on the record about this latest case.

Separately, sources familiar with the case told Fox News that Egyptian authorities have been providing to U.S. authorities information from their own investigation of Ahmed.

The implication is that the lack of direct access does not mean a total lack of information. In recent confirmation hearings, the president's nominee for CIA director was pressed about the Tunisian case and the problems the FBI faced.

When Sen. Marco Rubio, R-Fla., asked about access to al-Harzi, White House counterterrorism adviser John Brennan said: "We work with our partners across the board and when they are able to detain individuals, according to their laws, we work to see if we can have the ability to ask them questions, sometimes indirectly and sometimes directly."

The concern about access to suspects is one of many lingering worries lawmakers have about the terror attack of last year.

Tensions came to a head earlier this year, when then-Secretary of State Hillary Clinton clashed with Republicans over the issue of whether the administration tried to downplay the level of planning that went into the attack by initially casting it as spontaneous.

Lawmakers, though, continue to press for more details about the warnings the administration received about security in the months leading up to the attack and what President Obama did the night of Sept. 11.