Letters obtained exclusively by Fox News appear to show the State Department refused to get involved when the company tasked with protecting the U.S. Consulate in Benghazi, Libya, raised security concerns, the latest indication that warning signs may have been ignored in the lead-up to last month's terror attack.

The letters pertain to a dispute between Blue Mountain Libya, the security license holder in Libya, and its operations partner Blue Mountain UK, which trained and provided the local guards.

A source with knowledge of two State Department meetings -- one in June and a second in July -- told Fox News that Blue Mountain Libya felt the security provided by the UK partner was "substandard and the situation was unworkable."

But according to the source, when the Libyans tried to bring in a third party -- an American contractor -- to improve security, a State Department contract officer declined to get involved.

"The U.S. government is not required to mediate any disagreements between the two parties of the Blue Mountain Libya partnership," contracting officer Jan Visintainer wrote on July 10 to Blue Mountain Libya, adding that to date "contract performance is satisfactory."

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Asked about that letter Tuesday, State Department spokeswoman Victoria Nuland said the department's investigation likely would address the issue.

"Presumably, those kinds of questions will have to be looked at in the context of the work that we're doing," she said.

A representative with Blue Mountain UK has not yet responded to a request by Fox News for comment.

The July 10 exchange and the apparent warning that set it off are sure to be examined closely as both the State Department and Congress begin to scrutinize what may have gone wrong in the weeks and months preceding the attack, in which the U.S. ambassador and three other Americans were killed.

The House Oversight and Government Reform Committee plans to hold a hearing Oct. 10 on security in the region before the attack. Two members of that committee, Chairman Darrell Issa, R-Calif., and Rep. Jason Chaffetz, R-Utah, fired off a letter Tuesday to Secretary of State Hillary Clinton asking a string of security-related questions.

They detailed attacks and other security incidents in Benghazi starting in April and asked the State Department what measures it took to address the threat. Further, they claimed officials have told the committee of "repeated requests" for additional security that were turned down.

"Based on information provided to the committee by individuals with direct knowledge of events in Libya, the attack that claimed the ambassador's life was the latest in a long line of attacks on Western diplomats and officials in Libya in the months leading up to September 11, 2012," they wrote. "In addition, multiple U.S. federal government officials have confirmed to the committee that, prior to the September 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."

A State Department spokeswoman said Tuesday that Clinton plans to respond to the lawmakers' questions.

The letter to Clinton alleges 13 incidents that showed the deteriorating security situation on the ground -- one of which included workers with Blue Mountain. Weeks before the attack, the letter said, Libyan guards employed by the Blue Mountain Group were urged by their family members to quit over rumors "of an impending attack."

The letter included other incidents, which have been well documented, including the June attack on a convoy carrying the British ambassador. And it said "assailants" put an explosive device at the gate of the U.S. Consulate in early June, blowing a hole in the security perimeter.

The State Department, meanwhile, has stood by U.S. Ambassador to the U.N. Susan Rice in the face of criticism and calls for her resignation. Rice came under fire for claiming repeatedly the Sunday after the attack that it was a "spontaneous" reaction to protests over an anti-Islam film. The administration now acknowledges the assault was a coordinated terror attack.