The second day of the largest offensive since the 2001 US invasion of Afghanistan was characterized by painstaking house searches and sporadic fighting.

The troops cleared out booby-trapped houses one by one, advancing slowly down streets littered with thousands of homemade bombs and mines. Shots continued to ring out in some neighborhoods Sunday.

Lt. Josh Diddams, a Marine spokesman, said: “We're in the majority of the city at this point.” He also said the nature of the resistance has changed from the initial assault, with insurgents holding ground in some neighborhoods.