AUSTRALIA’S top defence official has warned that the mission to defeat the Islamic State or Daesh terrorists in Iraq could take five years.

Defence Secretary Dennis Richardson said the timing of the mission was debatable but it could take up to five years.

This contradicts the British Defence Secretary Philip Hammond who said the mission could be over within two years.

“I wouldn’t be putting my money on a one or two year time frame at this point,” Mr Richardson told a Senate Estimates Committee today.

“You would have to assume that in all likelihood it will take longer than two years rather than shorter.”

Senior US defence officials have stated that the mission could take up to five years.

Australia has more than 400 troops in Iraq at present including 300 “trainers” and security personnel based at Taji north of Baghdad in a so-called “advise and assist” mission with the Iraqi Army’s 76th Brigade.

Australian taxpayers have devoted more than $1 billion to the counter-ISIS mission in Iraq over the next 12 months.

Recent budget papers included funding for the following two years, but both Mr Richardson and Defence Vice-Chief Vice-Admiral Ray Griggs said further funding would be required.

Admiral Griggs said there had been no request from Iraq for Australian forces to accompany its forces on the battlefield as the Australians did in Afghanistan.

Mr Richardson also scoffed at reports that Daesh was a “state” and that it could acquire nuclear weapons although he conceded that it was well led militarily.

He said every terrorist organisation in the past two decades had aspired to a nuclear capability, either an atomic bomb or a “dirty” bomb.

“We would not see a risk in Iraq at this point in time in terms of Daesh and nuclear weaponry. “We think that’s a touch exaggerated,” Mr Richardson said.

Admiral Griggs said there were appropriate protective precautions in place for Australian troops in Iraq.

Some 200 of the 300 troops based at Taji were there for security reasons after eight diggers died in Afghanistan at the hands of those they were there to help.

“We can’t eliminate the risk.”

Admiral Griggs described the fall of Ramadi to ISIS forces as a “setback”.

“There is no doubt the performance of the Iraq security forces has been variable. There is no dodging that,” Vice Admiral Griggs said.

“It was variable during the fight for Ramadi.”

He said in the past three months there had been more progress by the Iraqi forces than by Daesh.

Admiral Griggs also revealed that RAAF aircraft had flown 968 missions over Iraq and had dropped 372 weapons against IS targets.

The RAAF tanker aircraft had flown 2194 hours and the Wedgetail command and control plane 1220 hours.