Two British fighter jets were flying over Iraq and ready to hit targets on Saturday, their first mission since parliament authorised strikes against Islamic State militants there, Britain's Ministry of Defence said.

Two Tornado jets left the Royal Air Force's Akrotiri base in Cyprus at 07:25 am, followed minutes later by a re-fueling aircraft, a Reuters witness said.

"We can confirm that . . . Royal Air Force Tornados continue to fly over Iraq and are now ready to be used in an attack role as and when appropriate targets are identified," said a Ministry of Defence spokesman.

Saturday's sortie was the first time British aircraft have flown over Iraq in an armed role since Islamic State militants swept across large areas of the north of the country in June and declared a caliphate including land already seized in neighbouring Syria.

The British aircraft joined a U.S.-led military coalition supported by some Gulf and European nations against the militant group.

Six Tornado jets, normally based at RAF Marham in England, have been based on the east Mediterranean island since August. They have been engaged in intelligence-gathering and reconnaissance over Iraq for the past six weeks.

Britain retains two military bases on Cyprus, a colony until independence in 1960.