International concern is mounting after a series of explosions hit the United Nations-run school in the northern Gaza Strip, killing at least 15 people and injuring dozens more.
U.N. and Gaza health officials confirmed the school at Beit Hanoun was shelled, but they could not confirm the exact number of casualties, nor the source of the attack.
The U.N. secretary-general said he was “appalled” by the carnage at a U.N. school in the northern Gaza Strip, where explosions killed and injured many women and children.
Ban Ki-moon was in the northern Iraqi city of Irbil on Thursday -- part of his shuttle diplomacy efforts in the region to reach a cease-fire between Israel and Hamas militants -- when he spoke of the attack.
Ban strongly condemned the shelling, which also killed U.N. staff members. He said circumstances of the attack were still unclear.
"I'm telling to the parties -- all the Israelis and Hamas and Palestinians -- that it's morally wrong to kill your own people," he said. "The whole world has been watching, is watching with great concern. You must stop fighting and enter into dialogue. Whatever grievances you may have, this is wrong. Why are you continuing to kill people? There are many other ways to resolve this issue without killing each other. I'm angry about what they are doing."
In New York, the secretary-general's deputy spokesman, Farhan Haq, said all the facts were not available in the immediate aftermath of the attack. “At this stage, we do not know - and I cannot verify - who attacked the compound.”
The school served as a shelter for hundreds of Palestinians fleeing the Israeli military's Gaza offensive.
A spokesman for the U.N. relief agency said it had tried in vain to arrange an evacuation of civilians from the school with the Israeli army, and noted reports of Hamas rockets falling in the area at the same time.
Gaza police said the school was hit by an Israeli shelling.
The Israeli military said its troops were fighting gunmen from Hamas, which runs Gaza, in the area and that it was investigating the incident.
The United Nations Relief and Works agency spokesman serving the Palestinian territories, Chris Gunness, said via Twitter that his agency had given the Israeli army "precise coordinates" of the shelter.
The Israeli Defense Forces released a statement saying "the Hamas terrorists in the area of Beit Hanoun" were "using civilian infrastructure and international symbols as human shields."
Watch related video report by VOA's Scott Bobb
The U.N. chief has called repeatedly on both sides to avoid attacking U.N. premises. More than 110,000 Palestinians have sought shelter in U.N. schools and other facilities since the fighting began.
Israel accuses Hamas militants of deliberately positioning their rocket launchers in Gaza’s densely populated residential areas, raising the risk of civilian casualties when Israel fires back.
In the last few days, the U.N. Relief and Works Agency [UNRWA] has found two separate weapons caches in facilities that it operates -- one in a vacant school and the other in a school where the rockets subsequently disappeared before authorities could seize them.
The U.N. condemned the incidents, saying they are unacceptable and that those responsible are turning the schools into potential military targets and endangering the lives of innocent persons seeking shelter there.
State Department concern
In Washington, State Department spokesperson Jen Psaki said the United States is “deeply saddened and concerned” about the incident and the rising civilian death toll. She urged both parties to intensify efforts to protect civilians, end the violence and reach a cease-fire agreement.
"This also underscores the need to end the violence and to achieve a sustainable ceasefire and enduring resolution to the crisis in Gaza as soon as possible.
"U.N. facilities in Gaza are sheltering more than 140,000 Palestinians, including many innocent children, and must remain safe, neutral sanctuaries for fleeing civilians," said Psaki. "We call on all parties to protect these facilities from the conflict and we have condemn those responsible for hiding weapons in United Nations facilities in Gaza. We urge all parties to respect civilian life and comply with international humanitarian law."
As Israeli strikes in Gaza continued Thursday and rockets fired by Hamas-led fighters in the enclave landed in Israel, both sides maintained their conditions for a cease-fire.
Palestinian health officials say more than 730 of their people have been killed since Israel began its campaign to halt Hamas rocket fire on July 8. Thirty-two Israeli soldiers and two Israeli citizens have died.
The Israeli military reported multiple rockets fired from Gaza on Thursday, including several that were said to have been intercepted by its Iron Dome missile defense system.
After meeting [Thursday] with British Foreign Secretary Philip Hammond, Israeli Prime Minister Benjamin Netanyahu said Hamas militants are using Palestinian civilians as human shields and complained Israel is being criticized for defending itself.
"This use of human shields is extraordinarily cynical, it is grotesque. It is inhuman. But what is equally grotesque is that Israel was condemned at the Human Rights Council," said Netanyahu.
Hamas leader Khaled Mashaal denied Wednesday the charge of human shields. During a news conference in Qatar he said Hamas would accept a temporary humanitarian truce to allow aid to reach civilians in Gaza. But he said it would not accept any agreement that did not end the suffering of Gaza residents.
Mashaal said, "Everyone wants us to accept a cease-fire quickly, but then what? They say we then should negotiate our demands. We reject this idea. We rejected it on the first day, and we will reject it in the future."
Hamas said Israel must lift its blockade of Gaza and cease all aggression as part of any cease-fire.
Israel says it wants Gaza to be de-militarized.
Kerry in Cairo
Meanwhile, U.S. Secretary of State John Kerry is in Cairo as he continues to push for a cease-fire solution. On Wednesday he had met with Netanyahu, Palestinian President Mahmoud Abbas and United Nations chief Ban Ki-moon. While he made no comments after those talks, he said earlier in the day that "some progress" had been made.
A spokeswoman for U.S. Secretary of State John Kerry says the school attack underscores the need to end the violence.
Kerry will stay in Cairo into Friday trying to broker a cease-fire. But a State Department official says the secretary is not in the Mideast indefinitely, and will determine if there is a willingness to stop the fighting.
Hamas leaders say they will not agree to a cease-fire unless Israel and Egypt end their blockades of Gaza.
Israel wants the rocket fire to stop and to destroy a network of cross-border tunnels used by militants.
Airlines Resume Flights to Tel Aviv
U.S. airlines resumed flights in and out of Israel's Ben Gurion International Airport on Thursday, after two days of cancellations brought on by the conflict in Israel and Gaza.
Delta, United and U.S. Airways all announced the decision to carry out scheduled flights Thursday.
The U.S. Federal Aviation Administration removed restrictions into Israel late Wednesday, and the European Aviation Safety Agency lifted its restrictions into Israel on Thursday.
Some European airlines, including Lufthansa and Swiss Air, are suspending flights into Israel for another 24 hours.
The FAA says it carefully reviewed new information along with the measures Israel is taking to mitigate potential aviation risks.
The bans went into effect Tuesday after rocket fire from Gaza hit near the airport outside Tel Aviv.
VOA's Scott Bobb contributed to this report from Jerusalem, and Margaret Besheer contributed to this report from the United Nations headquarters in New York.