Secretary of State John Kerry's proposals for a cease-fire that would halt the fighting in the Gaza Strip have been resisted by the Islamic militant group Hamas, who insist that any truce agreement must meet the group's main demand that a joint Israeli-Egyptian blockade of the territory be lifted.

"When it comes to the balance of power in this crisis between us and Israel, they are the executioners, the aggressors, the occupiers, the settlers, and we are the true owners of the land," Hamas leader Khaled Mashaal said Wednesday in a televised speech from his home-in-exile in Doha, Qatar. "We will not accept anything but the end of the siege."

The Wall Street Journal reported Thursday that diplomats from the U.S., Israel, and other Middle Eastern countries are reworking a cease-fire proposal made by Egypt's foreign ministry last week. The paper reports that the new proposal would call for both Israel and Hamas to cease military operations in the coming days before calling on the U.S. and the international community to begin talks on a long-term economic program for Gaza.

Hamas rejected the initial Egyptian cease-fire proposal on the grounds that it had not been consulted by Cairo, and claimed that the plan did not provide for the lifting of the blockade or the release of militant prisoners from Israeli custody.

The Journal reports that Hamas' demands to open up the movement of goods into Gaza are likely to be met with resistance by Israel unless it is allowed to monitor the trade for weapons bound for Hamas.

Meanwhile, Israeli military officials told The Journal this week that Hamas's fighters are better-equipped and better-trained than in previous clashes in 2009 and 2012, said an Israeli military officer who requested anonymity.

The militants are using a strategy of avoidance, relying on snipers and improvised explosive devices to hit Israeli forces rather than engaging in face-to-face fighting where they would be at a big disadvantage, he said. They have infiltrated Israel through five cross-border tunnels, even as the army moves to destroy others.

Israeli tanks and warplanes continued to bombard the Gaza Strip on Thursday. Israel said that three of its soldiers had died Wednesday, bringing the military's death toll to 32 since ground operations in Gaza began on July 17 with the aim of halting rocket fire from Gaza and destroying a sophisticated network of cross-border tunnels. Two Israeli civilians and a Thai worker in Israel have also been killed.

The 16-day conflict has claimed the lives of 736 Palestinians, most of them civilians, Palestinian health officials say.

Gaza health officials say at least 15 people were killed Thursday when Israeli tank shells hit a compound housing a U.N. school in the northern Gaza Strip. Gaza health official Ashraf al-Kidra said the victims were among hundreds of people seeking shelter in the school from heavy fighting in the area. At least 150 people were injured.

The Palestinian Red Crescent confirmed that seven people were killed by tank shells at the school in the northern town of Beit Hanoun.

U.N. Secretary General Ban Ki-moon released a statement through a spokesman condemning the bloodshed at the school. U.N. staff members were reportedly among victims killed in the attack.

Thursday's incident was the fourth time a U.N. facility has been hit in fighting between Israel and Palestinian militants in Gaza. UNRWA, the Palestinian refugee agency, has said it has found militant rockets inside two vacant schools, but has yet to confirm the latest reports of the deaths.

Six members of the same family and an 18-month-old infant boy were killed Thursday when an Israeli airstrike hit the Jebaliya refugee camp in the early morning hours, according to Gaza police and health officials. Twenty others were injured in the strike, they said, and rescuers were digging through the rubble of flattened homes, looking for survivors.

An airstrike on a home in the southern Gaza town of Abassan killed five members of another family, said Gaza health official Ashraf al-Kidra. Abassan is near Khan Younis, in an area that saw intense fighting on Wednesday.

Heavy fighting was reported along the border of central Gaza, according to Gaza police spokesman Ayman Batniji. Israeli troops fired tank shells that reached parts of the Bureij and Maghazi refugee camps. There were no immediate reports of injuries.

Clashes also erupted between Palestinian fighters and Israeli troops in the northern town of Beit Lahiya, and the sound of explosions was audible across the town, Batniji said.

Israeli naval vessels meanwhile fired more than 100 shells along the coast of Gaza City and northern Gaza, the spokesman said, adding that rescue teams were unable to operate in the area because of the heavy fire.

More than 2,000 rockets have been fired at Israel from Gaza since July 8, and the Israeli military says it has uncovered more than 30 tunnels leading from Gaza to Israel, some of which have been used by Hamas to carry out attacks.

Israel imposed the blockade in 2006 after Hamas and other militants abducted an Israeli soldier in a deadly cross-border raid. It tightened the siege in 2007 after Hamas seized power from forces loyal to Western-backed Palestinian President Mahmoud Abbas, but had eased some of the restrictions in recent years.

Egypt tightened its own restrictions last year after the overthrow of a Hamas-friendly government in Cairo and has destroyed many of the cross-border smuggling tunnels that sustained Gaza's economy, and which were also used by Hamas to bring in arms.

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The Associated Press contributed to this report.