GAZA CITY, Gaza Strip (AP) - The top Hamas leader in the Gaza Strip signaled Monday that the Islamic militant group will not agree to an unconditional cease-fire with Israel, while Israel's defense minister pledged to keep fighting "as long as necessary" - raising new doubt about the highest-level mediation mission in two weeks.
U.N. chief Ban Ki-moon and U.S. Secretary of State John Kerry were heading to Cairo on Monday to try to end the deadliest conflict between Israel and Gaza's Hamas rulers in just over five years.
Meanwhile, cross-border fighting continued unabated, with Israeli strikes leaving entire families buried under rubble and Hamas militants firing more than 50 rockets and trying to sneak into Israel through two tunnels, the latest in a series of such attempts.
Palestinian health officials said at least 550 Palestinians have been killed and 3,350 wounded since the new round of fighting started on July 8. Twenty Israelis, including 18 soldiers, were also killed and several dozen wounded, including soldiers.
On Monday, Israeli fighter planes struck homes across Gaza, burying at least three families under the rubble in at least four cases, said Ashraf al-Kidra, a Palestinian health official.
In one of the strikes, nine members of a single family were killed in Gaza City, he said. In another, 10 people of a family were killed in the southern Gaza Strip.
Also, rescuers going through the wreckage of a house targeted late Sunday retrieved 28 bodies in the town of Khan Younis, including at least 24 from the Abu Jamea family, according to al-Kidra and a local human rights group.
"Doesn't this indicate that Israel is ruthless?" said family member Sabri Abu Jamea. "Are we the liars? The evidence is here in the morgue refrigerators. The evidence is in the refrigerators."
Elsewhere, Israel tank shells hit the Al Aqsa Hospital in the central town of Deir el-Balah, killing at least four people and wounding 60, al-Kidra said.
A doctor at the hospital, Fayez Zidane, said the third and fourth floors and the reception area were damaged, and patients were evacuated to the lower flowers.
The Israeli military had no comment.
In fighting, the Israeli military said 10 Hamas infiltrators were killed after being detected and targeted by Israeli aircraft.
Hamas also fired 50 more rockets at Israel, including two at Tel Aviv, causing no injuries or damage. Since the start of the Israeli operation, Hamas has fired almost 2,000 rockets at Israel.
Israeli Defense Minister Moshe Yaalon said the Gaza military operation would have no time limit.
"If needed we will recruit more reservists in order to continue the operation as long as necessary until the completion of the task and the return of the quiet in the whole of Israel especially from the threat of the Gaza Strip," Yaalon told a parliamentary committee.
Israel accepted an Egyptian call for an unconditional cease-fire last week, but resumed its offensive after Hamas rejected the proposal.
Hamas says that before halting fire, it wants guarantees that Israel and Egypt will significantly ease a seven-year border blockade of Gaza.
Ismail Haniyeh, the top Hamas leader in Gaza, signaled Monday that Hamas is sticking to its position.
He said the aim of the battle is to break the 7-year-old blockade of the Palestinian territory.
The blockade was imposed by Israel and Egypt after Hamas overran Gaza in 2007. Over the past year, Egypt has further tightened restrictions, driving Hamas into a deep financial crisis.
Haniyeh said in a televised speech Monday that "we cannot go back, we cannot go back to the silent death" of the blockade.
He said all of Gaza's 1.7 million residents shared this demand.
"Gaza has decided to end the blockade by its blood and by its courage," he said. "This siege, this unjust siege, must be lifted."
Kerry left Washington early Monday for Cairo, where he will join diplomatic efforts to resume a truce that had been agreed to in November 2012.
Hamas remains deeply suspicious of the motives of the Egyptian government, which has banned the Muslim Brotherhood, a region-wide to which Hamas also belongs.
Israel invaded Gaza late last week, preceded by a 10-day air campaign. Air and artillery strikes have targeted Gaza's border areas in an attempt to destroy tunnels and rocket launchers.
Sunday marked the single deadliest day in Gaza since the conflict erupted on July 8, with more than 100 Palestinians killed, according to Palestinian health officials. Most died in the first major ground battle of the conflict, in Gaza City's Shijaiyah neighborhood, which Israel says is a major source for rocket fire against its civilians.
In response to the escalation, the U.N. Security Council expressed "serious concern" about the rising civilian death toll and demanded an immediate end to the fighting.
On Sunday evening, Hamas spokesman Mushir al-Masri in Gaza claimed his group had captured an Israeli soldier. An announcement on Gaza TV of the soldier's capture set off celebration in the streets of West Bank.
But there was no official confirmation or denial of the claim in Israel.
For Israelis, a captured soldier would be a nightmare scenario. Hamas-allied militants seized an Israeli soldier in a cross-border raid in 2006 and held him captive in Gaza until Israel traded more than 1,000 Palestinian prisoners, some of whom were involved in grisly killings, for his return in 2011.
Enav reported from Jerusalem.