The Australian man who killed himself and several others in a suicide bomb attack in Iraq last week is believed to be 18-year-old Melbourne man Adam Dahman.

But his family has denied that he was behind the Baghdad blast, which killed five people and injured 21.

Adam's mother told 7News there is no proof her son is the suicide bomber, and until there is evidence he is dead, the family refuse to believe it.

She said she spoke to her son last week, but could not confirm whether that was before or after the terror attack, which happened in the centre of the Iraqi capital last Thursday.

Australian suicide bomber believed to be Melbourne teenager Adam Dahman. Photo: Facebook More

Dahman is believed to have left Australia late last year, when he was just 17, and had been in Iraq ever since.

It is believed he had been fighting for the Islamic State terror group, who named him as Abu Bakr al-Australi online.

The group has since claimed responsibility for the bombing, and named Adam as their so-called martyr.

The Federal Government confirmed on Monday that an 18-year-old Melbourne man was behind the attack.

Attorney-General George Brandis said the man is the second Australian suicide bomber in the Iraq and Syria conflicts.

Thew federal government said it is working hard to prevent the involvement of radicalized Australian men in religious wars in the Middle East.