U.S. intelligence agencies have identified at least 500 ISIS fighters over the past two months moving into the war-torn North African state that became an al Qaeda safe haven following the ouster of Libyan dictator Muammar Gadhafi in 2011, according to American defense officials.

Since then, Libya has become a chaotic, largely ungoverned territory as large numbers of jihadists and militias operate in the country amid competing government factions.

Additionally, ISIS leaders have notified recruiters to urge foreign fighters wishing to join the group to consider traveling to Libya, as border controls in Turkey have tightened, making it more difficult to reach the group’s stronghold in Syria, said officials who spoke on condition of anonymity.

ISIS emerged in Libya in 2015, first in the eastern city of Darnah where it was ousted in July. Currently, its main stronghold is the costal city of Sirte, where its official radio, Al Bayan, began broadcasting in June.