SYDNEY - A former unionist and Australian political figure was Sunday questioned on his return from the Middle East where he is believed to have helped those fighting against the Islamic State group, reports said.

The Australian Broadcasting Corporation said it understood that Matthew Gardiner was stopped by customs officials early Sunday after flying in to the northern Australian city of Darwin via Sweden and Singapore.

The Australian Federal Police confirmed that its officers “spoke to a Darwin man today following his return to Australia”.

A police spokesman said the man, who was not named, was released without charge.

“Enquiries relating to his activities while overseas are ongoing and as such it is not appropriate to comment further at this time,” he added.

Gardiner, a former trade unionist and ex-president of the Northern Territory branch of the opposition Labor Party, reportedly left Australia early this year to join a Kurdish militia fighting IS.

Gardiner reportedly served as an Australian Army combat engineer in Somalia in the 1990s, but it is not known whether he engaged in fighting when in the Middle East.

Australia is involved in the US-led coalition against IS in Iraq and last year passed a law criminalising travel to terror hotspots, in an measure designed to stop militants from going to Iraq and Syria to fight.

But fighting for either side in the conflict in Syria and Iraq is understood to be punishable on return to Australia.

“Australians risk prosecution under Australian law if they fight in other countries,” the Department of Foreign Affairs says on its travel warning for Iraq.

Gardiner was removed as the Northern Territory chief of the Labor Party and suspended from the organisation after the news he had travelled to the Middle East emerged, the ABC said.

Federal Labor leader Bill Shorten expressed relief Sunday that Gardiner was “back home safe and sound”.

“But I’m concerned anyone thinks they should be getting involved in these foreign conflicts, no matter what their intentions,” he said, the ABC reported.

The Australian government has increasingly been sounding the alarm over radicalised citizens, with about 90 thought to be fighting with the Islamic State group in Iraq and Syria.