Israel's military announced Thursday that it had called up 16,000 reservists as the country's Prime Minister vowed to destroy tunnels used by the Islamic militant group Hamas to attack soldiers and civilians inside Israel.

"We have neutralized dozens of terror tunnels and we are committed to complete this mission, with or without a cease-fire," Benjamin Netanyahu said Thursday. "Therefore I will not agree to any offer that does not allow the military to complete this important mission for the security of the people of Israel."

Israel said that most of the 32 tunnels it has uncovered have now been demolished and that getting rid of the remainder will take no more than a few days.

The latest call-up brings the total number of reserve troops called up by Israel to 86,000.

An Israeli defense official -- speaking on condition of anonymity because he was not permitted to discuss the matter with media -- told the Associated Press that the purpose of the latest call-up was to provide relief for troops currently on the Gaza firing line. However, Israeli officials have also said they do not rule out broadening operations in the coming days.

The Associated Press also reported that Egyptian officials met Thursday with an Israeli envoy about Israel's conditions for a cease-fire, including disarming Hamas, according to a high-ranking Egyptian security official. The official spoke on condition of anonymity because he was not allowed to discuss the delicate diplomatic efforts.

The Times of Israel reported that Egypt is refusing to host a Palestinian delegation unless Hamas ceases fire. For its part, Hamas has said it will only halt fire once it receives guarantees that a seven-year-old Gaza border blockade by Israel and Egypt will be lifted. Meanwhile, The Times of Israel reported that Israeli's Security Cabinet met Wednesday and approved ongoing strikes against Hamas.

Israeli strikes in the strip continued Thursday, with witnesses saying that munitions hit the Omar Ibn al-Khatab mosque next to a U.N. school in the northern town of Beit Lahiya.

The strike in Beit Lahiya early Thursday damaged water tanks on the roof of a building near the mosque, sending shrapnel flying into the adjacent school compound, where dozens of Palestinians displaced by the fighting had taken shelter.

"The shrapnel from the strike on the mosque hit people who were in the street and at the entrance of the school," said Sami Salebi, an area resident.

Gaza health official Ashraf al-Kidra said at least 15 people were wounded, with three of them in critical condition.

Kifah Rafati, 40, was being treated for shrapnel injuries at the nearby Kamal Adwan Hospital. She said she and her six children had been sleeping in a classroom facing the mosque when the explosion went off. "There is no safety anywhere," she added.

Israel's military said it would investigate whether tank shells struck a United Nations-run school in a Gaza refugee camp Wednesday in an event that drew condemnation from the U.S. and the U.N.

Israeli government spokesman Mark Regev told the BBC that Israel would issue an apology if it determined that fire from its troops struck the school.

"We have a policy; we don't target civilians," Regev said. "It's not clear to us that it was our fire, but we know for a fact there was hostile fire on our people from the vicinity of the school."

Pierre Kraehenbuehl, chief of the U.N. aid agency for Palestinian refugees, told the Associated Press that Israel must try harder to ensure that civilians are not hurt, especially in Gaza, where 1.7 million people are squeezed into a small coastal territory. His agency has opened 80 of its schools to more than 200,000 Palestinians fleeing the violence.

"What maybe the world forgets ... is that the people of Gaza have nowhere to go," he said. "So when the fighting starts and they move, it is not as if they can cross a border to somewhere."

Israel has accused Hamas of using residents of Gaza as human shields by launching rockets from the territory's most densely populated cities.

U.N. Secretary-General Ban Ki-moon, using somewhat less diplomatic language that Kraehenbuehl, called the school shelling "outrageous" and "unjustifiable," and demanded an immediate humanitarian cease-fire, adding, "Nothing is more shameful than attacking sleeping children."

The U.N. Security Council was meeting Thursday to discuss the violence in Gaza, after calling on both sides earlier this week to reach a long-lasting cease-fire.

Gaza health authorities say at least 16 people were killed in the school attack and 1,360 Palestinians have been killed since the start of the offensive, though it is unclear how many were civilians and how many were Hamas militants. Fifty-six Israeli soldiers have died since the start of the offensive, as well as two Israeli civilians and a Thai worker.

On Wednesday, White House spokesman Eric Schultz told reporters the Obama administration expected a "full, prompt, and thorough investigation" into the shelling, but stopped short of directly blaming Israel.

"We are extremely concerned that the thousands of internally displaced Palestinians, who have been called on by the Israeli military to evacuate their homes, are not safe in these UN-designated shelters in Gaza," Schultz told reporters. "We also condemn those responsible for hiding weapons in the United Nations facilities in Gaza. All of these actions violate the international understanding of the UN’s neutrality."

The Associated Press contributed to this report.