Tony Abbott says the government is redoubling its efforts to stop Islamist extremists who have fought in Syria or Iraq entering Australia.
And for anyone who has a right to enter the country but is suspected of fighting in the Middle East, the prime minister's message was clear: we'll be watching you.
The government believes about 150 Australians had fought or were still fighting with opposition groups in Syria and beyond - and some had moved from supporting moderates to backing extremists such as Islamic State of Iraq and the Levant (ISIL, also known as ISIS).
The Sunni militant group has taken over key cities in northern Iraq and is in striking distance of the capital Baghdad, with Canberra worried Australians may now be involved in the fighting.
Foreign Minister Julie Bishop and Attorney-General George Brandis have both expressed concern about the threat posed when those fighters return to Australia.
Mr Abbott says the government is taking the threat seriously.
"We are redoubling our vigilance at our borders to try to ensure that jihadists do not gain access to our country, or are monitored if they have the right of access to this country," Mr Abbott told reporters in Canberra on Thursday.
Ms Bishop said Australians fighting with Middle Eastern militant groups would pose a danger if they return home.
"They're becoming radicalised, learning the terrorist trade, and if they come back to Australia of course it poses a security threat," she told ABC radio.
Ms Bishop says she has already cancelled a number of passports on the advice of intelligence agencies.
Labor's foreign affairs spokeswoman Tanya Plibersek described returning Australian fighters as a "very serious risk".
Overseas fighters returned well trained, radicalised, and with a "sick sort of street cred", she said.
"That allows them to convince other impressionable young people that perhaps going to fight is a good idea, or perhaps committing crimes here in Australia might be a good idea," she said.
Ms Bishop on Thursday announced Australia would provide $5 million in humanitarian assistance to help in Iraq, with the money going to the UNHCR and World Food Programme.
Asked if Australia should support the regime of Nouri al-Maliki, whose Shia-led government is accused of fanning anti-Sunni sectarian violence in Iraq, Ms Bishop said it was "not a good government".
Mr Abbott said he was disappointed the al-Maliki government had not been better at ending sectarianism.
"Nevertheless, the Maliki government is the nearest thing to a legitimate government that a country like Iraq currently has," he said.
