The official said the camps were located about 45 kilometers, or 28 miles, southwest of the central coastal city of Sirte.
The official was not authorized to speak in advance of an expected Pentagon announcement and confirmed the strikes on condition of anonymity.
The strikes were carried out overnight and were authorized by President Barack Obama, marking perhaps the final use of military force by a wartime president who intervened in Libya in 2011 as part of a coalition that ultimately toppled dictator Moammar Gadhafi.
At the time, Pentagon officials said they would further support counter-IS efforts if asked by Libya's provisional government.
Libya fell into chaos following Gadhafi's ouster and killing. The country remains divided between east and west, with no effective government and a multitude of rival factions and militias.
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