Israeli troops advanced into the crowded residential areas of Gaza City on Thursday, terrifying thousands of residents and sending them fleeing for their lives, according to the Associated Press.

In a search for Hamas fighters, Israeli soldiers thrust deeper into the city. Israeli troops are being backed by helicopter gunships, tanks and heavy guns.

It wasn't clear whether this would be a brief foray or signal a new phase in Israel's devastating offensive against Gaza's Islamic Hamas rulers.

Israel has balked at launching all-out urban warfare in Gaza City, where Hamas militants are more familiar with the lay of the land and Israeli casualties would could grow.

The offensive was launched on December 27 to stop rocket attacks by Hamas on southern Israel.