Militants of the Islamic State (IS) took full control of government buildings and sites in Libya's Sirte city — 450 kilometres (280 miles) east of the capitalTripoli in western Libya — the Libyan Bawabet Al-Wasat news website reported Friday.

The IS group — according to the website — established checkpoints on Thursday night near Harawa, a small village that is located 50 kilometres east of Sirte, forcing frightened residents to flee homes.

No specific numbers were provided for families who fled, though Al-Wasat reported they headed towards western parts of the country.

The IS's takeover of Sirte is the group's first major military success in war-torn Libya.

Libya has been ravaged by four years of civil war, with an internationally recognised government operating out of Tobrouk in the east and a rival Islamist coalition maintaining control of the official capital.

Mohamed El-Shami, a spokesman of the Islamist-led coalition, which controls Tripoli but lacks international recognition, announced earlier on Friday that his troops withdrew from Sirte airport, which is located close to the military base of Gardabiya.

"After [our troops] left, Islamic State group fighters entered the base which had been completely emptied of equipment, except for one military plane which is out of use," AFP quoted El-Shami as saying.

Sirte, the hometown of former Libyan leader Muammar Gaddafi, has been witnessing months of clashes between IS armed men and the Fajr Libya (Libya Dawn) militias which are part of the Tripoli coalition.