SYDNEY (AFP) - An Australian man has died after stepping on a landmine in Syria while fighting for Kurdish forces against the Islamic State in Iraq and Syria, his family said on Wednesday.

Mr Keith Harding said he learnt on Monday that his 23-year-old son Reece, who left Australia in May, died over the weekend during a nightime operation.

The devastated father told the Australian Broadcasting Corporation that he received a message telling him to call an overseas number.

When he did so, the man on the other line explained: "I'm sorry mate that Reece is gone... he's stepped on a landmine. He's dead."

Foreign Minister Julie Bishop, who did not confirm the death, said the family's heartbreak should act as a warning to other Australians.

"We urge young Australians in particular not to leave Australia and take up arms," she said.

Mr Harding said that after leaving his Gold Coast home, his son messaged the family to say he was overseas doing "humanitarian work".

They later learned he was fighting with the Kurds, with pictures of him in army fatigues, holding a gun, posted on Facebook.

"With all the information that's spread about on the Internet with people beheading people, killing children, raping and beating women, I think it really did get to him in the end," said his father.

"He felt that he wanted to do the right thing and try and stop it in his small way that he could."

A man who said he fought alongside Reece posted a tribute on a Lions of Rojava Facebook page, set up by supporters who recruit for Syrian Kurdish forces.

"His whole unit swore revenge for his death and will leave no stone unturned until those filthy ISIS rats are exterminated," the fighter posted.

"The people of Rojava will hold his name up high for the generations to come."

About 120 Australians are believed to be fighting in Iraq and Syria, the vast majority with militant groups. At least 30 have been killed, according to the Australian government.