In a letter to Secretary of State Hillary Rodham Clinton, Chairman Darrell Issa and Rep. Jason Chaffetz said their information came from "individuals with direct knowledge of events in Libya."
Issa, R-Calif. and Chaffetz, R-Utah said the Sept. 11 attack in Benghazi that killed Ambassador Chris Stevens and three other Americans was the latest in a long line of attacks on Western diplomats and officials in Libya in the months before Sept. 11.
The lawmakers said they plan a hearing on Oct. 10. They asked Clinton whether the State Department was aware of the previous incidents, and whether the level of security that was provided to the U.S. mission met the security threat, and how the department responded to requests for more security.
Referring to the Sept. 11 attacks, the letter said, "It was clearly never, as administration officials once insisted, the result of a popular protest."
The State Department has declined to answer questions about whether extra security was sought by officials in Benghazi ahead of the Sept. 11 attack. Clinton did, however, discuss security on Sept. 18, when asked whether measures were appropriate.
"Let me assure you that our security in Benghazi included a unit of host government security forces, as well as a local guard force of the kind that we rely on in many places around the world," she said.
"In addition to the security outside the compound, we relied on a wall and a robust security presence inside the compound. And with all of our missions overseas, in advance of September 11th, as is done every year, we did an evaluation on threat streams. And the Office of the Director of National Intelligence has said we had no actionable intelligence that an attack on our post in Benghazi was planned or imminent."
She added that diplomats "engage in dangerous work, and it's the nature of diplomacy in fragile societies and conflict zones to be aware of the necessity for security but to also continue the important diplomatic work that has to go on.
"There is risk inherent in what we do and what these brave men and women representing the United States are up against every single day," Clinton said, "and we do our very best to limit that risk by ensuring that our security protocols reflect the environments in which diplomats work and the threats that they are presented with."