What is the UK's military commitment in Iraq?
Ministers have said Britain's involvement in Iraq could last for months to come. But what is the UK actually committing to the operation?
Prime Minister David Cameron has insisted there will be no "boots on the ground", promising: "Britain is not going to get involved in another war in Iraq."
Compared to the intervention in Libya in 2011, this is on a "relatively small scale", said Shashank Joshi, senior research fellow at the Royal United Services Institute.
That engagement involved a "substantial naval component", Typhoon fighter jets and four times as many Tornados as currently being used in Iraq, he said.
"I think the UK is keeping its options open, deploying limited resources which could be ramped up", he said, "but for now it's on a relatively small scale compared with Libya".
BBC defence correspondent Jonathan Beale said Britain's role "could easily change again to more direct intervention".
First to arrive were RAF Lockheed C-130 Hercules transport planes - based at Brize Norton in Oxfordshire - which have been dropping emergency supplies, including water, food and solar lanterns, to civilians left stranded by the conflict. The first one was completed on 9 August. One delivery had to be aborted over fears people below could be injured by the cargo. The Ministry of Defence would not give precise numbers of aircraft involved.
To minimise the risk of aid hitting civilians, Panavia Tornado jets from RAF Marham in Norfolk were next to arrive, and are being used for surveillance to identify safe places for the air drops. Jonathan Beale said the Tornados could "easily switch to a bombing role", although such a move would need approval from the Cyprus government.
Four Boeing Chinook helicopters, based at RAF Odiham in Hampshire and deployed to RAF Akrotiri in Cyprus, remain on stand-by to carry out any airlift of refugees fleeing violence if necessary. The Chinooks can transport heavy loads, and could accommodate 70-75 people if an evacuation was attempted.
They had been expected to take part in a rescue mission of refugees from Mount Sinjar in northern Iraq, but a US special forces mission found there were fewer people stranded on the mountainside than had been first thought.
The reconnaissance operation in Iraq has been bolstered by the Royal Air Force's Boeing RC-135 Rivet Joint aircraft, which has been deployed alongside the Tornados. Defence correspondent Jonathan Beale said the US-supplied electronic surveillance aircraft was being used to help the US military identify potential IS targets. The Ministry of Defence said the aircraft, flown by 51 Squadron, had carried out a number of flights over the past few weeks, helping "build an understanding of the humanitarian situation in northern Iraq and the associated [Islamic State] threat".
Rivet Joint surveillance aircraft
Boeing RC-135W (Airseeker)
paid for three spy planes from US
3,900-mile range (6,500km)
131ft wingspan (40m)
21-27 mission crew: including up to 3 pilots, 2 navigators, maintenance technicians and intelligence operators
As well as the aircraft, troops from the 2nd Battalion Yorkshire regiment were sent into the Kurdish capital Irbil for 24 hours to prepare the ground for a possible rescue mission by the helicopters.
They have now left but British special forces are reportedly in northern Iraq.