The federal government is concerned a former Australian soldier was killed while fighting with rebels in Syria but admits it doesn't know why or when he joined the conflict.
Combat engineer Caner Temel, from Sydney, died two months ago after he travelled to Syria to fight against the war-torn country's ruling regime.
Assistant Defence Minister Stuart Robert said Mr Temel had served in the army for 17 months before going AWOL in September 2010, and being discharged a month later.
The former soldier had been given basic weapons training, and as an engineer would have done "a limited amount of explosives work".
However, the government did not know why or when he joined the Syrian conflict.
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"We know everything about him while he served with us but as soon as you leave the defence force you are a civilian," he told ABC radio on Wednesday.
"Once people choose to leave the military it's very difficult for us to keep tabs on them."
Mr Temel's involvement in the Syrian war was "deeply concerning", Mr Robert said, before pointing out that he left the military six months before the conflict started.
"When the fighting started he was well and truly a civilian," Mr Robert said.
Labor frontbencher Chris Bowen also expressed concern about the man's involvement.
"Of course any Australian who thinks it's sensible to go to Syria and engage in the terrible hostilities there is making a big mistake," Mr Bowen said.
