Libya's local Islamic State affiliate has detonated two car bombs at a checkpoint near the country's Siddra oil fields and clashed with fighters allied with the internationally recognised government there.

Ali al-Hassi, a spokesman for the forces that control the majority of Libya's oil fields, said  six of their fighters were killed in the attacks, along with five IS fighters in the coastal port town of Siddra.

The extremist group has long had its eye on the fields, which lie east of its coastal stronghold of Sirte.

In a statement circulated online, the group said the operation was named after one of their killed leaders, Abu Mughira al-Qahtani.

Al-Qahtani was allegedly killed by a US air strike two months ago in the eastern city of Darna.