"We are sending a small number of Chinook helicopters to the region for use if we decide we need further humanitarian relief options," said a statement from Prime Minister David Cameron's office.

"We have also agreed to transport from other contributing states some critical military re-supplies for the Kurdish forces."

Downing Street could not immediately comment on which states would be providing the supplies.

The statement was issued after British Foreign Secretary Philip Hammond had chaired a meeting of the emergency response committee COBR and following a telephone conversation between Cameron and Australian counterpart Tony Abbott.

British Tornado fighter jets were launched to provide surveillance support for its humanitarian aid effort to help refugees fleeing jihadist Islamic State (IS) fighters in northern Iraq, soon after making a second airdrop.

The Ministry of Defence (MoD) confirmed that the Royal Air Force (RAF) had sent Tornado aircraft from RAF Marham in south east England, fitted with reconnaissance pods.

The planes were bound for RAF Akrotiri in Cyprus, where they would be ready "to provide vital intelligence".

The MoD would not confirm how many aircraft had been sent, but the BBC reported three jets had taken off at 2.00pm (1500GMT).

Downing Street stressed that Britain's "focus remains the humanitarian situation", particularly those refugees trapped on Mount Sinjar.

Three UK aid drops have now taken place, with RAF planes delivering 3,180 re-usable water containers, filled with a total of 15,900 litres of clean water, and 816 solar lanterns.

"Meanwhile urgent planning to get those trapped on the mountainside to safety will continue in the coming days between ourselves and US, the Kurdish authorities and other partners," added a Downing Street spokesperson.