Australian suicide bomber kills three in Iraq

The first Australian suicide bomber in Iraq has reportedly killed three people and injured 90 others in Baghdad.

The Age has reported the Islamic State of Iraq and the Levant (ISIL) announced on an affiliated Twitter feed overnight that a man called Abu Bakr al-Australi had detonated an explosives vest near a Shiite mosque.

Iraqi forces have long feared ISIL would take its insurgency into the capital by sending in suicide bombers, despite the group's recent lightning advances coming to a standstill north of Baghdad.

The Australian's alleged involvement comes after ASIO this week expressed fresh concerns about fighters who have already returned home and may pose a terrorism threat.

ASIO believes roughly 150 Australians are involved with extremists in Syria and Iraq.

It's thought about 60 are fighting in the region.