BAGHDAD - Iraqi security forces, after more than of 40 days of intense fighting, on Thursday told residents to evacuate their homes in the northeast Shiite slum of Sadr City and to move to temporary shelters on two soccer fields.

The military’s call indicated the possibility of stepped-up military operations and came as Iraqi security forces raided a radio station run by backers of Shiite cleric Muqtada al Sadr. In the southern port city of Basra, militants launched rockets that struck a coalition base, killing two contractors and injuring four civilians and four coalition soldiers.

Sadr City has been a battleground since late March, enduring U.S. airstrikes, militia snipers and gunbattles between U.S. and Iraqi forces and the Mahdi Army, the militia loyal to Sadr.