The NT Labor party has sacked its president following revelations he has left Australia to join the fight against Islamic State.

Matthew Gardiner has been stood down as president and his Labor membership suspended, the party has announced in a statement that refers any further questions to Australian Federal Police.

It follows reports that Mr Gardiner has left Australia intending on joining Kurdish fighters in the battle against ISIL militants in Syria.

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Mr Gardiner was also the secretary of hospitality, childcare and emergency services union United Voice in the NT, as well as the treasurer of peak body Unions NT.

“Today the executive committee of the NT ALP has stood down Matthew Gardiner as president of the party and suspended his membership,” NT ALP secretary Kent Rowe said late on Sunday.

“Territory Labor will be making no further comment as there is an Australian Federal Police investigation.”

The 43-year-old served as Australian Army combat engineer in Somalia in the early 1990s.

The ABC reports that Mr Gardiner was able to leave the country because he was not on any watch list.

About 90 Australians are now thought to be overseas fighting with Islamic State or similar terrorist groups, which has prompted the government to repeat its warning against people joining the conflict.

A spokesperson for Attorney-General George Brandis said it was illegal for Australian citizens to support any armed group in Syria, even though the Australian Defence Force and Kurdish rebels may share a common enemy.

“It is illegal to fight in Syria for either side of the conflict,” the spokesperson said.

“If you fight illegally in overseas conflicts, you face up to life in prison upon your return to Australia.

“We know there are some Australians who think they’ve made the right choice in becoming involved in overseas conflicts, but that choice only adds to the suffering in Syria and Iraq and it’s putting those Australians and others in mortal danger.”

The spokesperson urged people concerned about the conflict to donate to charities.

The Australian Federal Police has refused to discuss any detail, saying the matter is part of an ongoing investigation.

Mr Gardiner recently befriended a woman on Facebook whose page is littered with support for Kurdish militias fighting Islamic State.

Colleagues contacted by the ABC had been suspicious, with Mr Gardiner not being seen for weeks and his mobile phone has been switched off.

Fight not for ‘cowboys’

Immigration and Border Protection Minister Peter Dutton said the fight against ISIL should be left to Australia’s military, not “cowboys” who put themselves in harm’s way.

“We don’t want to see cowboys running off participating in conflicts, whether or not they were trained or once part of the ADF,” Mr Dutton told Sky Television on Sunday.

“It’s just not helpful for people to run off on their own course believing they’re doing some good when potentially they’re getting in harm’s way.

“If we have to divert resources to provide support to them or to rescue them or if they’ve become captive themselves, it’s just not a helpful outcome.”

Mr Dutton says ISIL has shown it will ransom or kill foreign captives, knowing they are potent propaganda tools that guarantee international attention.

“We just don’t want to see Australians killed regardless of whether they’re well-intentioned or not,” he said.

– with AAP