Hospital officials say overnight clashes between U.S. and Iraqi forces and Shiite militants in Baghdad's embattled Sadr City district killed seven people and wounded 45.

The U.S. military had no immediate comment about the fighting that broke out late Thursday in the sprawling district of 2.5 million people. Sadr City is a stronghold of the Mahdi Army of anti-American cleric Muqtada al-Sadr.

Witnesses say clashes ended in the early hours of Friday. U.S. helicopter gunships reportedly struck targets in Sadr City.

The district has been the scene of daily combat between militants and Iraqi government and U.S. troops for the past month.