Last November's assassination of two Japanese diplomats in Iraq was probably a terrorist attack instead of a robbery, the Foreign Ministry said in a report issued Wednesday.

"It is conceivable that the incident was not a simple robbery, and the possibility is high that it was terrorism committed by those who had planned to kill them," says the report, submitted to the House of Representatives Foreign Affairs Committee.

The attack occurred some 30 km south of Tikrit in northern Iraq between 1 p.m. and 1:30 p.m. on Nov. 29, it says.

Based on testimony from local residents collected by U.S. forces in Iraq, four sport utility vehicles participated in the attack and assailants wearing helmets and civilian clothes in two of the vehicles fired submachineguns, killing the diplomats and their Iraqi driver.

U.S. forces and Iraqi police have probed the killings but have yet to identify the assailants, it says.

The report also rejects an earlier allegation that U.S. troops erroneously fired on the car.