JERUSALEM AND GAZA CITY — Israeli troops and tanks thrust into densely populated Gaza City from three directions Sunday, drawing Hamas fighters into fierce combat in an offensive expanded by a fresh deployment of army reservists.
High-rise apartments shook and smaller, targeted buildings crumbled under the force of Israeli artillery shelling and missiles fired from helicopters. Plumes of black smoke rose as Hamas fighters answered with mortar rounds, automatic rifles and grenades.
The Israeli military said it killed 40 Palestinian fighters in the Gaza Strip on Sunday. Palestinian medical officials put the death toll at 20 civilians and reported finding seven other bodies, presumably those of militants. Israel reported no casualties of its own.
The fighting was the heaviest since Israel attacked the Palestinian enclave Dec. 27 with the declared aim of halting years of rocket attacks on southern Israeli communities.
Troops moved into streets and buildings on Gaza City's northern, eastern and southern edges before dawn but pulled back after several hours, leaving it unclear whether Israel's leaders had ordered an all-out assault on the seat of Hamas' government and paramilitary force. The Mediterranean Sea borders the city on the west.
A decision to escalate the offensive probably would bring tens of thousands of Israeli reservists, who were called up late last month, into close urban combat with steep casualties on both sides.
Brig. Gen. Avi Benayahu said Sunday that the army had begun sending some reservists into Gaza, but he declined to say whether a new phase of the offensive was underway.
Prime Minister Ehud Olmert told his Cabinet in Jerusalem that Israel "is getting close to achieving the goals it set" in Gaza, but added that "patience, determination and effort are still needed" to subdue Hamas.
Israel's ground forces entered Gaza on Jan. 3, the eighth day of punishing airstrikes, and quickly surrounded urban areas. Sunday's advance on Gaza City, the first significant movement of ground forces in a week, followed an unusual public appeal by the operation's commander, Maj. Gen. Yoav Galant, for a political decision to strike harder.
Intelligence officials said at the Cabinet meeting that Hamas had suffered severe losses but was not finished fighting. Twenty rockets and mortar shells fell inside Israel on Sunday; one missile damaged an empty kindergarten in Ashdod.
Palestinian officials say 884 Palestinians have died in the Israeli assault, more than a third of them women and children.
Thirteen Israelis have died, three of them civilians hit by rockets in Israel.
As Israeli troops and tanks withdrew from Gaza City neighborhoods, hundreds of panicked residents fled, clutching small children and hastily packed bags after a sleepless night.
"I'm sure they'll be back," Mazin Ashi, 31, said outside his apartment building in Gaza City's Tal Al Hawa district.
He was tossing blankets and other belongings into the trunk of a taxi as his wife, Safaa, climbed into the back seat with their three small children. They were headed for her sister's home near the city's main hospital, an area presumed to be safer.
"Hurry up," Safaa called to him. "We need to get out of here while it's still quiet."
Israel had dropped thousands of leaflets over the city Saturday warning of a wider offensive. New leaflets fell from the sky Sunday urging residents to report the whereabouts of Hamas fighters and providing a phone number to call.
"Confidentiality guaranteed," the message in Arabic promised.
Abu Alouf is a special correspondent.