Israel-Gaza updates: US is 'strengthening' military force in Middle East

Hamas leaders are asking mediators of the cease-fire negotiations with Israel to present a plan based upon previous talks instead of engaging in new ones, according to a statement Sunday.

Hamas also appeared to decline to discuss the "new conditions" proposed to the cease-fire plan by Israeli Prime Minister Benjamin Netanyahu in July, saying Israel then "went on to escalate its aggression against our people and commit more massacres."

The new development in the ongoing cease-fire negotiations came after a diplomatic push from the United States, Egypt and Qatar for a new round of talks to take place between Israel and Hamas on Aug. 15 in either Doha or Cairo. Israel agreed to send a delegation, but Hamas had yet to respond –- until now.

The upcoming talks were widely seen as the last, best possible chance at securing an agreement between the warring parties.

-ABC News' Ghazi Balkiz, Nasser Atta

The Israel Defense Forces on Sunday ordered civilians in the al-Jalaa neighborhood of northern Khan Younis to evacuate as Israeli troops began raiding the area it alleges is being used by Hamas terrorists.

The IDF said the area -- part of a humanitarian zone the Israeli military had initially set up in the southwestern Gaza Strip -- was being exploited by Hamas "for terrorist activity" and is now considered "dangerous." As a result, the IDF said, the boundaries of the humanitarian zone would be adjusted to exclude the al-Jalaa neighborhood.

The move comes just days after the Israeli military launched a fresh assault on Khan Younis, ordering civilians to evacuate the heavily destroyed eastern districts, where many Palestinians had returned less than two weeks ago after the IDF’s last incursion into Gaza’s second-largest city in July, according to the U.N. Relief and Works Agency. The area was also once part of the designated humanitarian zone.

"Due to significant terrorist activity, exploitation of the Humanitarian Area for terrorist activity and rocket fire toward the State of Israel from the al-jalaa area, remaining in this area has become dangerous," the IDF said in a statement Sunday morning. "Accordingly, at this time, the Humanitarian Area will be adjusted. The adjustment is being carried out in accordance with precise intelligence indicating that Hamas has embedded terrorist infrastructure in the area defined as a Humanitarian Area."

The IDF said early warnings to civilians were being made to mitigate harm to the civilian population and keep civilians away from areas of combat.

-ABC News' Morgan Winsor

Leaders around the world have condemned an Israeli strike on a school in Gaza, making an appeal to the international bodies to stop the killing of civilians and protect displaced Palestinians. They also address the potential damage this attack has on the potential cease-fire negotiations.

"The deliberate killing of these huge numbers of unarmed civilians whenever the mediators' efforts intensified to try to reach a formula for a ceasefire in the Strip is conclusive evidence of the absence of political will on the part of the Israeli side to end this fierce war," the Egyptian foreign ministry said in a statement.

Qatar called for an independent international investigation into the strike and for full protection for displaced people.

"The State of Qatar has strongly condemned the Israeli occupation's bombing of a school sheltering displaced people east of Gaza city, which led to dozens of martyrs and injured, and deemed it as horrific massacre and brutal crime against defenseless civilians and a flagrant infringement of the fundamental precepts of international humanitarian law," Qatar said in a statement.

Turkey also called it "a new crime against humanity."

"This attack demonstrated once again that the Netanyahu Government intends to sabotage the negotiations for a permanent ceasefire. International actors who do not take steps to stop Israel are complicit in Israel's crimes," the Turkish foreign ministry said in a statement.

The European Union said it was "horrified" by the images of the strike.

"At least 10 schools were targeted in the last weeks. There’s no justification for these massacres We are dismayed by the terrible overall death toll," Josep Borrell High Representative of the EU said in a statement.

Francesca Albanese, United Nations Special Rapporteur, called Gaza the "largest and most shameful concentration camp of the 21st Century."

"Israel is genociding the Palestinians one neighborhood at the time, one hospital at the time, one school at the time, one refugee camp at the time, one 'safe zone' at the time. With US and European weapons. And amid the indifference of all 'civilised nations.' May the Palestinians forgive us for our collective inability to protect them, honoring the most basic meaning of intl law," Albanese said.

Scores have been killed following a strike on Al-Tabeen School in Gaza City early Saturday.

Al-Tabeen School is in Al Darj area of Gaza city and the school was housing hundreds of displaced persons, officials in Gaza said.

Many of the displaced people sheltering at the school had been performing dawn prayers at the time of the strike, according to the Government Information Office in Gaza.

Initial reports from Gaza officials said almost 100 people have been killed and dozens wounded, with an official casualty count expected to come from the Palestinian Ministry of Health.

"Today, an Air Force aircraft attacked, under the intelligence guidance of the Israel Defense Forces, the Shin Bet and the Southern Command, terrorists who were operating in a military headquarters located in the 'Al-Tabin' school complex near the mosque in Darje Tafah area, which is used as a shelter for the residents of Gaza City," read a statement from the IDF following the strike.

Gaza’s Civil Defence said two floors of the school were targeted: the first was housing women and the ground was a prayer hall for the displaced.

There were a total of “93 martyrs, including 11 children and 6 women, as a result of the massacre committed by the occupation against the displaced people in the Al-Tabaeen School in the Al-Daraj neighborhood," according to the Gaza Civil Defense.