Australian Prime Minister Tony Abbott is playing down the prospect of deploying Australian combat troops on the ground in Iraq, saying only Iraqis can save their country from Islamic State extremists.

However, he has left the door ajar to a further deployment.

"We'll be in a better position to judge what might be desirable down the track once we're in there," he told Macquarie Radio today.

Watch: Key: SAS could join Isis fight on ground

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Australia is close to reaching an agreement with the Iraqi government to allow a 200-member unit of special forces to advise and assist local security forces.

But military experts are now questioning whether the international coalition can defeat IS without a ground campaign, and have questioned its reliance on air strikes against the extremists.

Mr Abbott said Australia had an "absolutely crystal clear" mission in Iraq involving air strikes and the special forces advisers, when asked if the government would need to contribute ground troops to the conflict.

"Let's put that mission into practice, fully into practice, let's see how it goes," he said.

"What we can't do is save Iraq. Outsiders can't save Iraq. Only in the end Iraqis can save Iraq."

Australian Super Hornet combat aircraft are continuing missions over Iraq this week.

That follows the first two-aircraft sortie on Sunday, followed by four aircraft on Monday. However, no bombs dropped.

Defence Chief Air Chief Marshal Mark Binskin will brief the media on Iraq operations in Canberra this morning.

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Meanwhile, Mr Abbott said he would "red card" members of groups like Hizb ut-Tahrir, denying them entry into Australia

The radical Islamic group will hold a lecture against United States-led combat in Syria in Sydney's Lakemba on Friday night.

Mr Abbott said the group was engaged in "hate preaching" and members should not be allowed to enter Australia to attend such events.

"By all means let Australians who want to say stupid things to say stupid things but there's no point importing troublemakers from overseas to stir people up," he told Macquarie Radio.

"I am sorry we haven't red-carded these hate preachers before but it will happen and it will happen quickly."

Mr Abbott said the current law doesn't allow the government to ban Hizb ut-Tahrir unless the group engages in terrorism, even though it campaigns against Australian values.

New laws to be introduced before the end of the year will also make it illegal to promote terrorism.

Friday's lecture, titled The War to End a Blessed Revolution, will accuse the US of attacking the "noble Syrian revolution" by entering Iraq.

"America has initiated yet another war, rounding up its puppets and allies to attack the Syrian revolution, while using intervention in Iraq as a convenient excuse," the lecture's brochure says.

Hizb ut-Tahrir spokesman Uthman Badar said Mr Abbott was trying to silence political dissent.

"This does not come as a surprise," Mr Badar said in a statement.

"We have long exposed government attempts to silence dissent against its unjust and brutal foreign policies."

Mr Badar said there were no international speakers attending Friday's lecture.

The United States is leading an international coalition in a combat mission to suppress the activities of extremist group Islamic State.

Mr Abbott says Australia has no plans to enter Syria and is in Iraq at the request of the Iraqi government.

- AAP