Rebel leader in Syria has Aussie links

Foreign Minister Julie Bishop has repeated a warning about joining the fight in Syria after a key rebel leader who appears to be Australian spoke to British media.

Sky News has broadcast an interview with Sheikh Mostafa Mahamed, believed to be a key leader within rebel group Jabhat Fateh al-Sham (JFS), who confirmed the rebel group's campaign in Aleppo.

The broadcaster said Mahamed was in his mid-30s, well educated and spent many years in Sydney.

Ms Bishop didn't confirm whether the government was aware of Mahamed being in Syria, but said about 150 Australians had travelled to the Middle East to fight.

"I have continually urged Australians not to travel to Syria or Iraq to take part in the conflict there," she told reporters in Melbourne.

"And in the case of al-Raqqa province, it is actually a crime for an Australian citizen to be there without lawful excuse."

In the interview Mahamed explains how JFS split from al-Qaeda to allow dozens of disparate rebel groups in Syria to join forces against the regime of President Bashar al-Assad.

The interview came after images of a small boy in the back of an ambulance after being pulled from rubble in Syria's Aleppo featured around the world.