Israel launched a ground operation in Gaza on the 10th day of an offensive to stamp out rocket attacks from the Palestinian enclave, the army said.
"Following 10 days of Hamas attacks by land, air and sea, and after repeated rejections of offers to deescalate 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.
Israel will pay 'high price'
Israel will pay a "high price" for launching a ground invasion of the Gaza Strip, the Palestinian Hamas movement said on Thursday night.
"The start of the Israeli ground attack on Gaza is a dangerous step, the consequences of which have not been calculated," said Hamas spokesman Fawzi Barhum in a statement.
"Israel will pay a high price and Hamas is ready for the confrontation."
UN urges Israel to spare Palestinian civilians
UN Secretary-General Ban Ki-moon urged Israel to "do far more" to spare Palestinian civilians after it launched a ground offensive in Gaza on Thursday.
"I regret that despite my repeated urgings, and those of many regional and world leaders together, an already dangerous conflict has now escalated even further," Ban told reporters.
The UN chief described as "appalling" the death of four boys killed by Israeli strikes Wednesday on a Gaza City beach.
"I urge Israel to do far more to stop civilian casualties. There can be no military solution to this conflict," he said.
Egypt has also weighed in, denouncing Israel's "escalation" in Gaza after the start of a ground offensive late on Thursday, and again demanded both sides accept a Cairo proposed truce.
Israel launched Operation Protective Edge on July 8 to stamp out rocket attacks from Gaza and the army said the new operation will include ground and air assaults.
"This stage of operation 'Protective Edge', led by the IDF's Southern Command, will include close coordination between IDF units including infantry, armoured corps, engineer corps, artillery, and intelligence combined with aerial and naval support," it said.
"This effort will also be supported by the Israeli Security Agency (ISA) and other intelligence organisations," the army added.
At least 240 Palestinians have been killed in Israeli air strikes since July 8, many of them children, medics in Gaza said, with a NGO based in the coastal enclave saying 80 percent of the deaths are civilians.