Gaza City  - An Israeli strike on a UN-school in northern Gaza killed at least 42 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 dozens more were injured in the strike on the al-Fakhoura school in the Jabaliya refugee camp, north of Gaza City.

UNWRA Spokesman Chris Gunness said he was unable to immediately give details he was unable to reach his own staff in Gaza.

Hassanein was unable to say whether a tank shell or a missile hit the school, but several Israeli army tanks are stationed some three kilometers east and north of the camp, on its outskirts.

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)