Israeli ground forces made their deepest foray yet Sunday into Gaza's most populated area, with tanks rolling into residential neighborhoods and infantry fighting urban warfare in streets and buildings with Hamas militants who kept up their rocketing of southern Israel.

An Israeli army spokeswoman said residential neighborhoods in Gaza are riddled with homemade bombs and booby traps, including mannequins placed at apartment entrances to simulate militants and rigged to explode if soldiers approach.

The army "is advancing more into urban areas," said the spokeswoman, Maj. Avital Leibovich. "Since the majority of the Hamas militants are pretty much in hiding in those places, mainly urban places, then we operate in those areas."

Early Monday, Israeli navy gunboats fired more than 25 shells at Gaza City, setting fires and shaking office buildings, including the local bureau of The Associated Press. The military said that in general, the targets are Hamas installations but had no immediate information about the shelling that began just after midnight.

Before daybreak Monday, at least one militant was killed in an Israeli airstrike in northern Gaza, where a battle was in progress, hospital officials said.

Nearly 900 Palestinians killed so far
Gaza medical officials say at least 870 Palestinians, about half of them civilians, have been killed in the conflict that began Dec. 27 with Israeli airstrikes on Hamas buildings, as well as suspected rocket launch sites and smuggling tunnels on the Egyptian border. Thirteen Israelis, including 10 soldiers, have died.