WASHINGTON - State Department officials in May denied a request from the US Embassy in Tripoli to allow a security team to continue using an official US DC-3 aircraft, suggesting they could charter a plane instead, an unclassified email obtained by Reuters shows.

The email dated May 3, carrying the subject line "Termination of Tripoli DC-3 Support," was copied to Christopher Stevens, the US ambassador to Libya who was killed with three other Americans in an attack on the Benghazi mission on September 11 this year.

The email is among documents US investigators are examining to determine whether requests before the Benghazi attack for security improvements at U.S. diplomatic posts in Libya were denied by State Department headquarters.

The email says Under Secretary of State for Management Patrick Kennedy "has determined that support for Embassy Tripoli using the DC-3 will be terminated immediately."

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