Foreign Minister Julie Bishop says Australians fighting with extremists in Iraq and Syria “is one of the most disturbing developments” in domestic security for some time, as the number of Australians believed to be participating in the conflicts reached 150.

Ms Bishop told the ABC's Insiders program on Sunday that the government was concerned that a number of Australians who were travelling through Lebanon to reach Syria were now moving from Syria into Iraq to join Sunni militants.

She said the government had cancelled several passports for Australians seeking to fight in Iraq, as it had done when it was reported that Australians were seeking to join or come back from fighting in Syria.

“We are receiving reports that they are also in Iraq where ISIS is fighting the Iraqi security forces and so we are doing what we can across government,” Ms Bishop said.