British drones deployed to counter Islamic State jihadists in Iraq will also be used for surveillance over Syria, the government in London said Tuesday.

Foreign Secretary Philip Hammond announced last week that unmanned Reaper drones were being re-deployed from Afghanistan to the Middle East.

Britain's parliament has authorised air strikes in Iraq, where Tornado fighter jets are part of an international operation conducting bombing raids on IS group targets, but not in Syria.

Defence Secretary Michael Fallon said in a written statement to parliament that the drones would start operations "very shortly".

"As well as their operations over Iraq, both Reapers and Rivet Joint surveillance aircraft will be authorised to fly surveillance missions over Syria to gather intelligence as part of our efforts to protect our national security from the terrorist threat emanating from there," he said.

"Reapers are not authorised to use weapons in Syria; that would require further permission."

During the debate on strikes against targets in Iraq last month, Prime Minister David Cameron said he would return to parliament to seek fresh permission if it was necessary to extend the action to Syria.

But he also stressed that it could go ahead without a parliamentary vote in the event of an urgent humanitarian situation.

As well as sending eight jets which are flying sorties out of Cyprus, Britain is supplying weapons, ammunition and training to Kurdish Peshmerga forces.

The IS group controls large areas of territory in Iraq and Syria, where it has declared an Islamic "caliphate", prompting a US-led coalition to launch air strikes which have so far lasted several months.