The CIA is subjecting operatives on the ground during last year's terrorist attack in Benghazi, Libya to monthly polygraph tests as part of an effort to keep the details of a clandestine mission there secret, a new report said.

CNN reported that dozens of CIA officials were in Benghazi when four Americans, including U.S. Ambassador Christopher Stevens, were killed during a Sept. 11, 2012 terrorist attack on the U.S. Consulate there. Citing unidentified sources, the network reported that 35 Americans were on the ground during the attack, including about two dozen CIA employees.

What exactly the CIA officials were doing there remains unclear. And CNN says the spy agency is stepping up its polygraph tests to ensure that details aren’t leaked to either Congress or the media, using monthly polygraphs rather than doing so every few years, which is standard practice.

The CIA insisted Thursday that the polygraphs were not intended to hide information from lawmakers investigating the Beghazi attack.

“CIA employees are always free to speak to Congress if they want,” CIA spokesman Dean Boyd said. “The CIA enabled all officers involved in Benghazi the opportunity to meet with Congress. We are not aware of any CIA employee who has experienced retaliation, including any non-routine security procedures, or who has been prevented from sharing a concern with Congress about the Benghazi incident.”

But some on Capitol Hill were not swayed by the spy agency’s defense. One Republican went as far as to suggest that the Obama administration may have been moving weapons from Libya to rebel forces in Syria who are fighting against President Bashar al-Assad.

“Was the CIA annex being used to facilitate these transfers?” Rep. Frank Wolf, R-Va., asked from the House floor on Thursday. “If these weapons were not being transferred to other countries like Syria, where exactly did they end up?”

The CIA did not respond to questions about supplying weapons to Syria.

White House officials have dismissed the GOP’s probe of Benghazi as a “phony scandal,” accusing Republicans of exploiting a tragedy to score political points. GOP leaders counter that questions about what happened that day remain nearly a year after the attack.

Republicans charge that the administration mishandled the matter and misled the public about what happened in Benghazi just ahead of the presidential election. Administration officials initially attributed the violence to a spontaneous protest sparked by an anti-Islam video, before weeks later admitting that it was a terrorist strike.