An American jihadist carried out a suicide truck bomb attack against Iraqi forces involved in an operation to recapture the city of Tikrit, the Islamic State group said Tuesday.

"The brother Abu Dawud al-Amriki (may Allah accept him) launched himself with his explosives-laden truck against a gathering" of Iraqi forces and militiamen, an IS radio bulletin said.

The report gave no details on the man's identity.

It claimed that dozens of Iraqi forces were killed and wounded in the blast, but no other sources could immediately confirm.

Pro-IS social media accounts said the attack was carried out Monday near Samarra, the other main city in Salaheddin province, and released a picture they said was of Abu Dawud al-Amriki.

He is masked with only a pair of dark eyes visible. He also wears a microphone, suggesting the group may issue a video of the militant later.

Samarra is controlled by the government and has been the launchpad for a broad military operation which officially began Monday to wrest back Tikrit -- further north up the Tigris River -- from the jihadists.

Army commanders say the jihadists have been slowing the advance by resorting to guerrilla tactics, such as car bombs, booby traps and sniper fire.

IS, which took control of swathes of Iraq last year and also holds parts of Syria, frequently uses foreign fighters for suicide missions.