Australian fighter jets have flown their first combat mission over Iraq, with a pair of F/A-18F Super Hornets returning safely to base without attacking any targets.

The mission came as Dutch and Belgian warplanes also joined the US-led coalition targeting Islamic State fighters who have seized territory in the country's north and west.

A Belgian F-16 dropped a guided bomb on a "terrorist element", and France also announced it was increasing the number of sorties its planes would fly.

Chief of the Defence Force Mark Binskin said the two Australian jets were armed, but did not launch air strikes.

In a brief statement on social media, he said both returned safely to their base in the United Arab Emirates.

"2 F/A-18F completed 1st armed combat mission in Iraq. No munitions expended. Returned safely to base," he tweeted.

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A statement from the Australian Defence Force confirmed the mission, saying the "aircraft conducted an air interdiction and close air support mission over northern Iraq overnight".

Defence Minister David Johnston said the planes were providing important air cover for local forces, flying missions of between six and 10 hours.

Former Army Chief Peter Leahy said it was normal for a fighter jet to fly a mission and return without having dropped any bombs.

"You would expect something like this to happen, particularly as we want to minimise collateral damage," he said.

"We don't want to be hitting the wrong target.

"What we have seen from ISIS over the last week or so is that they've made themselves a much harder target... they've dispersed, they're adapting camouflage patterns, they've moved back inside the cities and getting close to the forces and holding on.

"We need to make sure we don't exacerbate the problem with support from the locals by causing them damage."

This is 'the first of many iterations for this mission'

Labor frontbencher Chris Bowen said it was a mission "in defence of the defenceless".

"This is a humanitarian mission that is important for the peace and freedom of the people of Iraq and also for global stability and global peace," he said.

Sorry, this video has expired F/A-18s complete first combat operation over Iraq ( Andrew Greene )

Federal Government frontbencher Mitch Fifield told Sky News the Government was pleased to assist Coalition partners in Iraq.

"I think all Australians will be happy that the first foray by ADF personnel has concluded safely," he said.

"The mission obviously will have many iterations. This is the first."

The flights are the first since the Federal Government authorised Australian airstrikes on Islamic State targets in Iraq on Friday.

Two hundred Australian special forces soldiers will also advise Iraqi and Kurdish troops on the ground, pending final legal sign-off from the Iraqi government.

Last week an Australian reconnaissance jet and refuelling plane began flying over Iraq in support of the US-led coalition fighting Islamic State (IS) insurgents.

The United States has been building an international coalition for an air campaign against IS since first launching air strikes in August.

The US has also been carrying out air strikes in Syria, where Kurdish forces are currently holding out against an Islamic State siege in the border town of Kobane.

Over the weekend a female Kurdish suicide bomber blew herself up in an attack on Islamic State outside the town, a British-based monitoring group said.