The United States is increasingly concerned about the growing presence and influence of the Syria-based Islamic State movement in Libya, according to US officials and a State Department report.
The officials said what they called "senior" Islamic State leaders had travelled to the country, which is whacked by civil war, to help recruit and organize militants, particularly in the cities of Derna and Sirte.
Since late January, Islamic State militants have carried out attacks, including a car bombing and siege at the Corinthia, a luxury hotel in Tripoli, and an attack on the Mabruk oilfield south of Sirte, according to a report circulated this week by the State Department's Diplomatic Security Bureau.
The militants also posted on the Web images of the beheading of 21 abducted Egyptian Coptic Christians on a Libyan beach.
The State Department document said estimates of the number of Islamic State fighters operating in Libya ranged from 1000 to 3000.
Around 800 fighters were based in the Derna area alone, the report said, including up to 300 who previously fought in Syria or Iraq.
U.S. officials said that because of its strategic position, Libya had become a springboard for would-be fighters from across North Africa wanting to link up with the Islamic State. They could travel from there to Syria for frontline experience.