Aboout 20 armed men killed one person and wounded another on Saturday morning, a SCIRI official told AFP.
"Armed men attacked our headquarters with rocket-propelled grenades (RPGs), killing one person and wounding another," the SCIRI official said.
"The 20 masked and armed men attacked our headquarters around 8 am (0400 GMT) with RPGs, grenades and small arms," the injured man, Haitham Mehdi Ibrahim, said from his hospital bed.
The city's hospital, located 60 kilometres northeast of Baghdad, confirmed it had received one dead and one wounded.
The building's guards traded fire with the gunmen, with the attack coming two days after an assault by anti-occupation forces on local police that killed at least 11 police officers on Thursday.
The offensive coincided with armed strikes in cities across northern and central Iraq that left around 90 people dead on Thursday.