BAGHDAD, April 25 (UPI) -- Overnight violence in northern Baghdad's Sadr City area claimed at least 11 lives and wounded 36 others, an Iraqi Interior Ministry official told CNN Friday.

Recent battles in the area have involved U.S.-backed Iraqi forces and fighters loyal to radical Shiite cleric Moqtada Sadr. The U.S. military launched overnight airstrikes on targets in the neighborhood, the official said.

Sadr City has been enveloped in similar clashes for several weeks.

In a statement read at Friday prayers, Sadr urged his followers to "wage open war against the Americans" while refraining from attacks on Iraqis, The New York Times reported.

"If we have threatened with an open war until liberation, we have meant by it a war against the occupier," he said.

The U.S. military also reported that one soldier was killed Thursday by a roadside bomb south of Baghdad.