The Islamic State jihadist group has seized control of the airport in the city of Sirte after forces of a Tripoli-based Libyan government withdrew, a spokesman said Friday.

Mohamed al-Shami, whose government is not recognised by the international community, said its forces pulled out late Thursday from the airport which had "fallen into the hands of the IS organisation".

IS itself said it captured the airport, which is also a military base, in a message posted on Twitter.