Violence in Baghdad claimed the lives of more than 20 people on Wednesday as fighting between Iraqi troops and Shia militias threatened to undermine efforts by Moqtada al-Sadr, the radical Shia cleric, to contain the conflict.

The clashes occurred in Sadr city, a Baghdad slum, as the capital was placed under a vehicle curfew to mark the fifth anniversary of the fall of the regime of Saddam Hussein.