Israeli marines clashed with Hamas gunmen Sunday in the first reported ground incursion in the latest Gaza offensive. It follows a heavy night of violence during which 18 members of the same family were killed in the deadliest single attack on the besieged enclave in days of shelling. A Palestinian woman and a girl, aged 3, were killed in Israeli raids early on Sunday, Gaza's Health Ministry said. Hours earlier, the ministry said the house of Gaza's police chief was bombed by the air, resulting in many casualties. The Israeli army said at least four soldiers were "lightly injured" on Sunday, as they attacked a site in northern Gaza the army said was being used to launch long-range rockets. Giving details of the naval commando operation early on Sunday, Lieutenant Colonel Peter Lerner, an Israeli military spokesman, said four members of the force were wounded in exchanges of fire with Hamas fighters. Hamas said its fighters had fired at the Israeli force offshore, preventing them from landing in northwest Gaza. Lerner said the forces had "completed their mission." Following the operation, Israel later dropped leaflets on northern Gaza urging residents to leave the area, ahead of an expected wider attack on the area. "Those who fail to comply with the instructions will endanger their lives and the lives of their families. Beware," read a leaflet dropped by the Israeli military in the town of Beit Lahiya, where 70,000 Palestinians live. Civilians in three of its 10 neighborhoods were warned to evacuate their residences and move south, deeper into the Gaza Strip, by 12 p.m. In response to the warning, thousands fled their homes Sunday, the sixth day of an offensive that Palestinian officials say has killed at least 160 people, including about 135 civilians – among them some 30 children. More than 1,000 have been wounded, according to Gaza’s Health Ministry. The Gaza Interior Ministry, in a statement on Hamas radio, dismissed the Israeli warnings as "psychological warfare" and instructed those who left their homes to return and others to stay put. The warnings cited roads that residents could use safely and said Israeli forces intended to attack "every area from where rockets are being launched." The Israeli military did not say in the leaflet whether the strike would include ground troops.

Civilians flee northern Gaza

It was the first time Israel had warned Palestinians to vacate dwellings in such a wide area. Previous warnings, by telephone or so-called "knock-on-the-door" missiles without explosive warheads, had been directed at individual homes slated for attack. At least 4,000 people fled Beit Lahiya and crowded into eight United Nations-run schools in Gaza City on Sunday, a spokesman for the U.N. Relief and Works Agency said. Some arrived on donkey carts filled with children, luggage and mattresses, while others came by car or taxi. One man, still in his pajamas, said some residents had received phone calls warning them to clear out. "What could we do? We had to run in order to save the lives of our children," said Salem Abu Halima, 25, a father of two. Despite mounting international pressure to cease fire, Israel-Palestinian hostilities showed no signs of abating. A Hamas source commenting on the air strike against the police chief's home on Saturday said the officer, Tayseer Al-Batsh, was in critical condition. All of those killed in the air strike, which television footage showed was reduced to piles of rubble, were members of the police chief’s family. Ashraf Al-Qidra, spokesman for the Gaza Health Ministry, said 45 people were wounded in the bombing.

Ground invasion remains open