PRAGUE (AFP) - The European Union Wednesday urged Israel to open a humanitarian corridor to Gaza as outrage mounted over attacks on UN-run schools and child victims of an offensive which has killed nearly 700. "The presidency of the EU is deeply concerned by the increasing number of civilian casualties and the worsening humanitarian situation in Gaza," said a statement in Prague, which currently leads the bloc, as the death toll crossed 694. "There is a dire need in Gaza for basic supplies, including food, medicines, water and electricity," it said, as Israel said it would suspend bombings for three hours every day. "We continue to call on both sides to immediately implement a comprehensive ceasefire to ease the suffering of civilians in both Israel and Gaza," the EU said. Cristina Gallach, a spokeswoman for EU foreign policy chief Javier Solana, roundly condemned an Israeli attack on a school in Jalabiya operated by the UN refugee agency, in which at least 43 people were killed. She said this was "unacceptable" as "civilians found themselves targeted as they were trying to seek refuge." Two other schools were also targeted. "We learn with consternation of the shelling of a UNRWA school in Gaza, which killed several dozen civilians, including women and children, who had fled to escape the fighting," French foreign ministry spokesman Eric Chevallier said in Paris. Almost a third of the 694 Palestinians killed in Israel's offensive are children, with most killed since the start of a ground offensive after a week of aerial bombardment, medics said on Wednesday. The proportion of civilians killed has risen dramatically since Saturday when ground troops joined the assault on the Hamas rulers of Gaza after a week of aerial and naval bombardment. A total of 220 children have been killed since Operation Cast Lead was unleashed on December 27, according to Gaza emergency services chief Moawiya Hassanein. Humanitarian agencies fear civilian casualties will rise further as the battle moves into the most densely populated areas of Gaza, one of the most crowded places on Earth. "Of increasing concern is the number of children and their families fleeing the fighting and bombardment or seeking refuge because their homes have been destroyed or damaged," the Save the Children agency said on Wednesday. Civilians have nowhere to flee from the conflict. The borders are sealed off under an 18-month-old Israeli blockade, and buildings designated by the United Nations as safe shelters have been hit by artillery shelling.