London (AFP) - British warplanes flew their first mission over Iraq since parliament authorised strikes against Islamic State jihadists, but returned without bombing on Saturday, the Ministry of Defence in London said.

Royal Air Force Tornado GR4 combat jets returned to Britain's RAF Akrotiri base on Cyprus without dropping any of their load of Paveway IV laser-guided bombs, after a seven-hour mission that began before dawn from the Mediterranean island.

"On this occasion no targets were identified as requiring immediate air attack by our aircraft," a ministry spokesman said.

However, the jets' surveillance gathered information that will "help acquire potential targets for future operations, either by aircraft or Iraqi ground forces," the spokesman said.

British lawmakers on Friday voted overwhelmingly to join the US-led air strikes in northern Iraq following a formal request for help from the Iraqi government.

Six British Tornados have been based on Cyprus since last month, from where they have been conducting reconnaissance missions, but the vote allows their role to expand to include striking IS targets.

The campaign against the Islamist group gathered pace this week, as Belgium and Denmark agreed to join the bombing and Britain's lower house of parliament voted in favour of air strikes in Iraq.

On Saturday, a fresh round of bombings by the US, Saudi Arabia, Jordan and the United Arab Emirates damaged an IS-held airfield, a garrison and a training camp near the group's headquarters in Raqa, the Pentagon said.

In Iraq, a fighting position and four armed vehicles were hit, it added.

IS's brutal abuses against civilians, rival fighters and Arab and Western hostages, as well as its success in recruiting Western members, have triggered international alarm.

British Prime Minister David Cameron said Saturday the RAF was there to "play our part".

"We are one part of a large international coalition," he said during a visit to Didcot, southern England.

"But the crucial part of that coalition is that it is led by the Iraqi government, the legitimate government of Iraq, and its security forces. We are there to play our part and help deal with this appalling terrorist organisation."

Besides the Tornados, the RAF also has a Rivet Joint spy plane in the region which is stepping up surveillance efforts to identify potential targets.