The United Nations has called for a probe into the Israeli attacks that killed at least 45 civilians in UN-run schools in the Gaza Strip.

"These tragic incidents need to be investigated, and if international humanitarian law has been contravened, those responsible must be held accountable," Max Gaylard, UN humanitarian coordinator for the Palestinian territories said Tuesday.

On the eleventh day of an Israeli offensive against the strip, the Israeli army targeted three UN-run schools.

Palestinian medics said Tuesday that most of the victims were people who had been given shelter inside the schools, adding that several dozen individuals were also wounded in the strike.

"These deaths highlight the tragic reality of the situation in Gaza that for civilians, neither homes nor UN shelters are safe," said Gaylard.

UN official added that there are no safe shelters for the 1.5 million civilian population of the coastal strip.

The United Nations Relief and Works Agency (UNRWA) decried the attacks, saying it had provided Israeli authorities with the GPS co-ordinates of all UN installations in Gaza including the attacked elementary schools.

At least 635 Palestinians have so far been killed and 3,040 others have been wounded in the Israeli attacks. The majority of the victims are women and children.

PKH/HGH