Several senior commanders from the so-called Islamic State have moved to Libya from Iraq and Syria in recent months, according to a top Libyan intelligence official.
Representatives from 23 countries, including the US and UK, met in Rome on Tuesday to discuss the growing threat from Islamic State (IS) in Libya.
IS took control of Sirte last year.
Disagreements between rival administrations in the country have hampered efforts to fight IS.
Islamic State took control of the city of Sirte last year. Sirte was the hometown of the former Libyan leader Muammar Gaddafi. The Islamist group is believed to have received support from some loyalists of the former regime.