The congressmen said based on information provided to the Committee on Oversight and Government Reform "by individuals with direct knowledge of events in Libya" the Sept. 11 attack that killed U.S. Ambassador Christopher Stevens and three other Americans "was the latest in a long line of attacks on Western diplomats and officials in the country."
"It was clearly never, as administration officials once insisted, the result of a popular protest," Issa and Chaffetz wrote.
"In addition, multiple U.S. federal government officials have confirmed to the committee that, prior to the Sept. 11 attack, the U.S. mission in Libya made repeated requests for increased security in Benghazi. The mission in Libya, however, was denied these resources by officials in Washington."
The lawmakers said they will hold a hearing of the oversight panel Oct. 10 to review possible security failures in Libya.
Issa and Chaffetz's letter reveals in addition to multiple threats, two former security guards threw homemade bombs over the consulate's security fence April 6.
The Obama administration has been criticized by Republicans and others for initially saying the Sept. 11 attack occurred spontaneously during protests against an anti-Islam video produced in the United States and posted on the Internet. By Friday, National Intelligence Director James Clapper said it had been determined the assault was a "deliberate and organized terrorist attack."
White House press secretary Jay Carney, asked by a reporter at his daily briefing if he could shed any light on the allegations of the 13 threats and attacks, noted the State Department is conducting an accountability review and the FBI is investigating the attack itself.
"It's natural, obviously, as this investigation continues and more information is learned in that process, that new information is presented and we endeavor to convey that to you where appropriate and possible," he said.
Asked if he could provide a yes or no answer to whether there were warnings, Carney said he was limited in what he could say because of the twin investigations.
"It is certainly, broadly speaking, a known fact that Libya is in transition," he said. "It is a known fact that in the eastern part of Libya there are militant groups, and in the country as a whole but especially in eastern Libya, a great number of armed individuals and militias -- that is one of the legacies of the revolution there and the civil war."
Asked by a reporter, who said it's been established the FBI has not been in Benghazi, if the president has concerns about the pace of the FBI investigation, Carney replied Obama "is committed to ensuring that those who are responsible for the deaths of four Americans in Benghazi, including our ambassador, are brought to justice. He is committed to the investigation into what happened being full and comprehensive and uncovering all the facts that we need to know about that event."