JERUSALEM (AFP) -- Israel began a ground operation in Gaza late Thursday on the 10th day of an offensive to stamp out rocket fire from the Hamas-run enclave that has cost 240 Palestinian lives.
The assault follows a brief humanitarian truce and despite an appeal from Washington, which cautioned against a land assault, for Israel to do more to protect civilian lives.
Hamas warned Israel would pay a "high price" for its escalation.
"Following 10 days of Hamas attacks by land, air and sea, and after repeated rejections of offers to de-escalate the situation, the Israel Defence Forces (army) has initiated a ground operation within the Gaza Strip," it said in a statement.
The army said the aim of the operation is to protect Israeli lives and crush Hamas, which controls the Gaza Strip.
The objective was "to establish a reality in which Israeli residents can live in safety and security without continued indiscriminate terror, while striking a significant blow to Hamas's terror infrastructure."
Israel launched "Operation Protective Edge" on July 8 but confined it to air attacks until late Thursday.
Shortly before the announcement of the ground operation, Egypt sharply criticized Hamas, saying the group could have saved dozens of lives had it accepted a Cairo-mediated truce.
Hamas had rejected the ceasefire intended to start on Tuesday and continued firing rockets at Israeli cities.
"Had Hamas accepted the Egyptian proposal, it could have saved the lives of at least 40 Palestinians," Egypt's Foreign Minister Sameh Shoukri said.More children killed
At least five more Palestinian children were among the dead in Israeli strikes Thursday, as a rehabilitation hospital in Gaza City was targeted by tank fire, after having already been hit earlier this week.
Earlier, a rocket fired from Gaza hit southern Israel exactly as a UN-requested five-hour truce ended at 3:00 p.m., and the Israeli military resumed its air strikes.
Two Palestinian brothers aged 7 and 8 who were playing on a Gaza rooftop with their 10-year-old cousin were among five children killed shortly after the truce expired, medics said.
Israeli tanks also shelled Al-Wafa hospital injuring several nurses, said director Basman Alashi who voiced concern for the 14 patients trapped in the rehabilitation centre who are paralysed or in coma.
"There is no place safe in Gaza! If a hospital is not safe, where is?" said Alashi, whose hospital has been hit at least three times since the conflict erupted.
The army says more than 1,000 rockets fired from Gaza have struck Israel since last week and 283 have been shot down by the Iron Dome air defense system.
On Thursday the air force shot down a Hamas drone near the southern city of Ashkelon close to the Gaza border, the second this week, the military said.
Meanwhile, the UN's Palestinian refugee agency said it had launched a probe after finding 20 rockets hidden in one of its vacant schools in Gaza, calling it was a "flagrant violation" of international law.
With regional efforts to broker a lasting ceasefire gathering pace in Cairo, an Israeli official said earlier that the Jewish state had agreed a truce with Hamas to begin at 0300 GMT Friday.
However Hamas denied the claim, with spokesman Sami Abu Zuhri telling AFP: "The news about a ceasefire is incorrect. There are continuing efforts but no agreement until now."Civilian casualties
In Washington, State Department spokeswoman Jen Psaki called on Israel to protect civilians, after dramatic footage of children killed on a Gaza beach in an Israel strike Wednesday.
"We ask (Israel) to redouble their efforts moving forward to prevent civilian casualties, given the events of the last couple of days," Psaki said.
"We believe that certainly there is more that can be done."
On the diplomatic front, President Mahmoud Abbas met Egyptian leader Abdel Fattah al-Sisi in Cairo to discuss ways of ending the Israeli offensive on Gaza.
Hamas, the main power in Gaza, is demanding that Israel lifts its eight-year blockade of the coastal enclave, the opening of the Rafah border crossing with Egypt and the release of Palestinian prisoners.
Thursday's short-lived truce allowed medical aid to be transported into Gaza and gave residents of the battered enclave a chance to leave their homes to stock up on goods.
In Gaza City, the streets immediately filled with honking cars and traffic jams, and outside banks, hundreds of people massed by ATMs to withdraw money to buy supplies.
Just moments before the humanitarian truce began, Israeli tank fire killed three people in southern Gaza, Palestinian medics said.
The Gaza-based Palestinian Center for Human Rights says more than 80 percent of those killed in Israeli air strikes have been civilians.
Turkish Prime Minister Recep Tayyip Erdogan accused Israel of seeking a "systematic genocide" of the Palestinians.