"Our brother Abu Mohammed al-Almani advanced in a booby-trapped vehicle carrying 1.5 tonnes of explosives on a gathering of the Safavid army west of the city of Baiji," it said.
"God made it easy for him to make the murtadeen (another derogatory word used by IS to designate the army) suffer, leading to dozens of deaths and injuries among them.
What was left of them fled. Two Hummers and a bulldozer were burned," IS said.
The jihadist group controls Baiji, about 200 kilometres (125 miles) north of Baghdad, but the country's largest oil refinery just north of it has been one of the 11-month-old Iraqi conflict's most relentless battles.
Dozens of Germans have died fighting for IS in Syria and Iraq, several of them in suicide operations.
EU Justice Commissioner Vera Jourova said recently that an estimated 5,000 to 6,000 Europeans were fighting with jihadist groups in Syria.