GAZA CITY, Gaza Strip (TheBlaze/AP) — While Thousands of Palestinian residents of the northern Gaza Strip fled their homes on Sunday and sought safety in U.N. shelters, heeding warnings from the Israeli military about impending plans to bomb the area, a defiant Hamas is urging them to stay.

While Thousands of Palestinians Flee Northern Gaza, a Defiant Hamas — Accused of Using Them as Human Shields — Urges Civilians to Stay

Palestinians flee their homes to take shelter at the United Nations school in Gaza City, Sunday, July 13, 2014. (Image source: AP/Hatem Moussa)

Hamas, an Islamic militant group sworn to Israel’s destruction, continued to fire rockets into Israel throughout the day. It urged people in northern Gaza to stay in their homes and has so far rejected proposals for a cease-fire as unsatisfactory.

“They want us to put down our arms and leave the resistance,” said Moussa Abu Marzouk, a top Hamas official, on his Facebook page. “They started the battle, and we will stay on our land and fight to protect our future.”

While Thousands of Palestinians Flee Northern Gaza, a Defiant Hamas — Accused of Using Them as Human Shields — Urges Civilians to Stay

Palestinians flee their homes to take shelter at the United Nations school in Gaza City, Sunday, July 13, 2014. (Image source: AP/Hatem Moussa)

But Israel accuses Hamas of using Gaza’s civilians as human shields, putting people in the densely populated territory in danger.

“The leadership of Hamas and the other organizations has chosen — at a time when they are using the population of Gaza as human shields — to hide underground, to flee abroad and to deliberately put civilians in the line of fire,” Israeli Prime Minister Benjamin Netanyahu said.

Despite Israel’s claims, the international community, including many of Israel’s allies, have begun to express concerns about the growing civilian death toll.

In Vienna, U.S. Secretary of State John Kerry spoke Sunday with Netanyahu and highlighted U.S. concerns about the “escalating tensions,” the State Department said.

Kerry “described his engagement with leaders in the region to help to stop the rocket fire so calm can be restored and civilian casualties prevented, and underscored the United States’ readiness to facilitate a cessation of hostilities,” the State Department said.

Many of the airstrikes have been on the homes of wanted Hamas militants, putting their families at risk. In an attack on Saturday, the target of one such airstrike, Gaza’s police chief, survived, while 17 members of his extended family were killed. But Hamas says it is largely unscathed, and Palestinian medics say most of the dead have been civilians.

While Thousands of Palestinians Flee Northern Gaza, a Defiant Hamas — Accused of Using Them as Human Shields — Urges Civilians to Stay

Palestinian mourners gather around the grave of a member of the al-Batsh family who were killed in Saturday’s Israeli airstrike, during a funeral procession in Gaza City on Sunday, July 13, 2014. The strike hit the home of a cousin of Gaza police chief Taysir al-Batsh and damaged a nearby mosque as evening prayers ended Saturday, killing at least 18 people, wounding 50 and leaving some people believed to be trapped under the rubble, said Palestinian Health Ministry official Ashraf al-Kidra. (Image source: AP/Lefteris Pitarakis)

Amid the diplomacy, Israel said it was pushing forward with preparations for a possible ground invasion of Gaza. Thousands of troops have massed along the border in recent days.

“We don’t know when the operation will end,” Netanyahu told his Cabinet on Sunday. “It might take a long time.” He said the military was prepared “for all possibilities.”

Israel launched the offensive last Tuesday in what it said was a response to heavy rocket fire out of Hamas-controlled Gaza. The military said it has launched more than 1,300 airstrikes, while Palestinian militants have launched more than 800 rockets at Israel. The Palestinian Health Ministry in Gaza says 166 people have been killed, including dozens of civilians. There have been no Israeli fatalities, though several people have been wounded, including a teenage boy who was seriously wounded by rocket shrapnel Sunday.

While Thousands of Palestinians Flee Northern Gaza, a Defiant Hamas — Accused of Using Them as Human Shields — Urges Civilians to Stay

A picture taken from the southern Israeli city of Sderot shows rockets being fired from the Gaza strip into Israel, on July 13, 2014. A rocket fired from Syria hit the Israeli-occupied sector of the Golan Heights on July 13, 2014, falling on open ground and causing no casualties, an army spokeswoman told AFP. (Image source: AFP/Jack Guez/Getty Images)

The outbreak of violence follows the kidnappings and killings of three Israeli teenagers in the West Bank, the kidnapping and killing of a Palestinian teenager in an apparent revenge attack, and wide-ranging Israeli moves against Hamas militants and infrastructure in the West Bank. Hamas has demanded that hundreds of recently arrested activists be freed as part of a cease-fire.

Early Sunday, the Israeli air force dropped leaflets around the northern Gaza town of Beit Lahia ordering people to evacuate their homes. Israel says much of the rocket fire has come from the area, and overnight Sunday, the military carried out a brief ground operation on what it said was a rocket-launching site that could not be struck from the air. Four Israeli soldiers were lightly wounded before returning to Israeli.

The U.N. refugee agency for Palestinians, UNRWA, said some 17,000 Palestinians had headed to special shelters set up in 20 United Nations schools in Gaza.

“The fact that in a span of almost a few hours, 10,000 people sought refuge in these 15 schools is an indication to the difficult situation on the ground,” said Sami Mshasha, a UNRWA spokesman.

Some raced by in pickup trucks, waving white flags. “Once we received the message, we felt scared to stay in our homes. We want to leave,” said one resident, Mohammed Abu Halemah.

Shortly before nightfall, Israel carried out a series of airstrikes in the northern Gaza town of Beit Lahia. Hamas’ Al-Aqsa TV station reported four airstrikes in a 10-minute span, and a large plume of black smoke could be seen over the area from the Israeli border. There were no immediate reports of casualties.

Egypt said President Abdel Fattah el-Sissi spoke to the U.N. chief Ban Ki-moon. El-Sissi’s spokesman quoted Ban as praising Egyptian efforts to halt the fighting and affirming that “Egypt is the most capable party to effectively participate in reaching a calm between the two sides.” Netanyahu’s office declined comment on diplomatic efforts.

Other countries were also involved. Germany’s foreign minister said he would head to the region on Monday, while French President Francois Holland tried to rally Arab and Muslim leaders to push for a cease-fire.

Hollande tried to rally other leaders to push for a cease-fire in Gaza, holding telephone talks over the weekend with Turkish Prime Minister Recep Tayyip Erdogan and Tunisian President Moncef Marzouki.

Marzouki spokesman Adnane Mancer said the French and Tunisian presidents agreed that Marzouki would try to talk to Hamas leaders and urge a cease-fire, while Hollande would try to do the same with other parties. A French presidential official said Hollande was talking to Israeli, Palestinian and other Arab officials.

On Sunday, Palestinians with foreign passports began leaving Gaza through the Erez border crossing. Israel, which cooperated in the evacuation, said 800 Palestinians living in Gaza have passports from countries including Australia, Britain and the U.S.

Rawan Mohanna, a 21-year-old chemistry major at the University of Texas, said she had arrived in Gaza with her family a month ago because her older sister was getting married to a Gazan.

Mohanna, who lives in Dallas, said her family is now returning to the U.S. with mixed feelings because her newlywed sister and other relatives were staying behind.

“It’s bittersweet that we get to leave but they are still there and they can’t get out,” she said.

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