Story highlights U.S. Special Forces are taking the fight to ISIS inside Libya

U.S. surveillance flights are operating from the Sicilian island of Pantelleria

The U.S. estimates between 4 and 6,000 ISIS fighters are now in Libya

Misrata, Libya (CNN) It is a tiny, remote aircraft hangar, carved in the Sicilian rock decades ago, but now home to a new and vital front for the United States against ISIS.

U.S. Special Forces and surveillance flights are operating on the ground and over Libya as the West moves to boost security operations in the country to bolster Libya's increasingly desperate fight against ISIS.

Surveillance flights over the country's 2,000-kilometer (1,240-mile) coast have been in operation from the remote Sicilian island of Pantelleria for over a year, and Special Forces have recently increased their presence on the ground. Witnesses and Libyan officials told CNN they are in evidence near the city of Misrata, with an estimated dozen soldiers operating out of a base near the city.

The U.S. presence in Libya was acknowledged by Pentagon officials in the past few days, who admitted groups of Special Forces were "meeting a variety of Libyans." The teams are said to be in action around the capital Tripoli, as well as Misrata and the east of the country.

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The U.S. publicly only supports the latest of the three groups who claim the right to govern the country -- the Government of National Accord, led by Fayez al-Sarraj and recently installed by the United Nations. But the presence of these Special Forces teams in the strongholds of the other two groups claiming to be the country's legitimate government shows that America retains wider private contacts.

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