Gaza City  - An Israeli strike on a UN school in northern Gaza killed at least 46 Palestinian civilians in the deadliest single incident since Israel launched its offensive in the Strip 11 days ago, health officials said.

Gaza emergency services chief Mo'aweya Hassanein told reporters that more than 150 injured in the strike in the playground of the al- Fakhoura school in the Jabaliya refugee camp, north of Gaza City.

Between 800 and up to 1,000 civilians had been taking shelter in the camp's boys' elementary school, run by the UN's agency for Palestinian refugees (UNWRA).

They had fled from heavy fighting on the camp's outskirts between local militants and Israeli soldiers.

While an UNWRA staff member in Gaza said it was an artillery shell which hit right next to the school, other witnesses said both tank shells and missiles had struck the school ground.

Most of those killed had been outside at the time the projectile struck, while people inside were also injured by shrapnel.

Local Palestinian television showed shrapnel holes and black soot marks on the school's wall, and bloodstains and shoes and slippers scattered on the ground just outside. Windows and doors were badly damaged.

A local UNWRA spokesman, Adnan Abu Hasna, said the school had been been waving a blue UN flag. UNWRA had also passed the GPS coordinates to Israel of its schools and shelters in Gaza. Despite this, four UNWRA schools had been caught in the crossfire over the past days.

Heavy fighting has been taking place between local militants and the Israeli ground troops stationed on the outskirts, with the tanks shelling in the directions from where Palestinian gunmen have been firing anti-tank missiles and mortar shells at the troops.

Israel F16 fighter jets have also been covering the ground troops, firing at the locations from which militants have been firing at the Israeli soldiers.

Witnesses said it was Israeli fighter jets which struck the UN school, adding the strike came shortly after Palestinian militants fired mortar shells from an area near the school at the Israeli forces stationed north of the camp.

An Israeli military spokesman said he was checking the reports.

Hassanein said the death toll in the Gaza Strip since the beginning of the Israeli air and ground offensive on December 27 now topped 600, while over 2,600 have been wounded. (dpa)