Israel pressed its assault against the Gaza Strip with a series of strikes on Saturday, killing at least 31 Palestinians, about half of them civillians, including four children, medical officials said.

Of the 31 killed on Saturday, 16 were civilians and the rest fighters, according to hospital staff and the Islamist Hamas movement.

One of the dead civilians was a mother who was preparing breakfast for her children when she was hit by gunfire, relatives and medical workers said. A girl and her brother were also among the dead.

The fighting was concentrated in and around the crowded Jabaliya refugee camp in northern Gaza, where Israeli special forces crept in just after midnight followed by a wider incursion involving tanks and helicopters.

Doctor Muawiya Hassanein, head of Gaza emergency medical services, said at least 31 people were killed, most of them by a "great number of rockets fired by Israeli planes" in and around the camp and town of Jabaliya.

Witnesses also reported clashes in the nearby Tufah neighbourhood in northern Gaza City.

The high death toll makes Saturday's operation the deadliest raid on Gaza in several months and comes at the end of a sharp four-day escalation of violence that has killed nearly 66 people.

The dead included at least four children and two women, medics said, including a 12-year-old girl and her 11-year-old brother, who relatives said were killed by shrapnel as they slept inside their home.

At least 10 fighters were killed in the operation, including five from the Islamist Hamas movement and another two from Islamic Jihad, as several missiles slammed into the town and fighters exchanged fire with Israeli soldiers.

At least five Israeli soldiers were wounded, the army said.

An Israeli army spokeswoman said troops had killed at least 15 Palestinian fighters."

Gaza fighters meanwhile fired at least 30 rockets at southern Israel, army radio reported.

The latest deaths came after tens of thousands of Gazans poured into the streets of the Hamas-run territory on Friday to protest against Israeli raids.

And it followed a warning by Israeli officials of a major ground operation.

Palestinian president Mahmud Abbas expressed concern at the "dangers of an Israeli escalation" in the Gaza Strip and urged both sides to halt their attacks, a statement from his office said late on Friday.

Defence Minister Ehud Barak said earlier Israel was considering the possibility of launching a widescale ground operation in Gaza.

The attacks from Gaza injured a handful of people and killed a civilian on Wednesday, the first Israeli since May to die from the rocket fire.

The chief of Israel's left-wing Meretz party, Yossi Beilin, said Hamas had offered a truce around Gaza over the past two weeks but the overtures had been rejected by the Israeli leadership.

Agencies