Abbott warns Australians in Iraq 'radicalised and militarised'

Prime Minister Tony Abbott has again raised concerns over Australians fighting alongside militants in Iraq, saying the government will ensure they won’t come back and “cause mayhem”.

Prime Minister Tony Abbott has again raised concerns over Australians fighting alongside militants in Iraq (AAP)

His comments come as Sunni militants advance through western Iraq after seizing a strategic Syrian border crossing.

Some 100 Australians have travelled to Syria and Iraq to join the jihadist cause, Mr Abbott told Channel Seven’s Sunrise program today.

“This is very worrying, because they’re being radicalised and militarised through that experience,” he said.

“The important thing is to ensure our borders are secure. Border security is not just about stopping illegal boats. Border security is also about ensuring that we don’t have people coming back to Australia and potentially causing mayhem.”

Mr Abbott said Australians engaged in violence overseas were acting illegally and faced serious consequences on their return.

“They will feel the full force of our law,” he said.

His comments follow those made by US Secretary of State John Kerry, who spoke in Cairo about the need for the country's leaders to rise above sectarianism.