Israeli tanks entered Gaza on Thursday night after Prime Minister Benjamin Netanyahu ordered a ground invasion, a major escalation in a ten-day offensive that has already killed more than 230 Palestinians.
Witnesses in Gaza reported heavy bombing from jets, warships and artillery stationed along the border, with much of the firing directed at northern Gaza. Electricity was cut off across a large swathe of the strip, though it was unclear why.
Peter Lerner, an Israeli military spokesman, said: "The military objectives are twofold.
"To strike Hamas as a terrorist organization, which is globally labeled, so that they do not have the motivation to continue this aggression against Israel.
"And second of all to strike the terrorist infrastructure, the rockets, the tunnels, the mechanisms that they are using to strike and attack Israel."
Palestinian officials said 19 Palestinians were killed in heavy fighting overnight, bringing the death toll to 259, including 39 children. More than 1,900 Palestinians have also been injured.
The Israeli military said that one soldier was killed in the north of Gaza on Friday, but the circumstances surrounding the death remain unclear. One Israeli was killed by rocket fire from Gaza earlier this week.
A statement from Netanyahu and Defense Minister Moshe Ya'alon described the invasion as focused on destroying tunnels connecting Gaza to Israel.
Speaking to Al Jazeera, Hamas spokesperson Fawzi Barhoum said that the ground operation amounted to "stupidity" and that the Israeli army would "pay a high price."
Sami Abu Zuhri, another spokesman for the group which controls Gaza, said: "It does not scare the Hamas leaders or the Palestinian people. We warn Netanyahu of the dreadful consequences of such a foolish act."
Speaking to Al Jazeera, Diana Buttu, a former legal adviser to the Israeli-Palestinian peace negotiations, said: "I think it's high time that the Palestinian Authority go and sign on to the International Criminal Court and start charging Israel with war crimes. This isn't the first time this has happened."
"They [Israel] shouldn't be allowed to behave like they are above the law, and treat Palestinians like they are beneath it."
On Thursday morning, a group of gunmen tried to enter southern Israel through a tunnel from Gaza, the army said, and eight of the 13 attackers were killed. Hamas claimed responsibility for the operation.
It was the second such incident in the past ten days.
Israel’s Operation Protective Edge “will deal significant damage to the infrastructure of Hamas and other terrorist organizations in the Gaza Strip," the army said.
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The escalation came not long after a five-hour humanitarian cease-fire requested by the United Nations, which gave residents a brief chance to venture outside before the bombardment resumed.
Both sides largely stopped firing, and people ventured out to markets, grocers, barbers and banks, which opened for the first time in more than a week.
Media reports on Thursday afternoon, attributed to Israeli officials, suggested that a ceasefire had been agreed upon and would take effect the next morning.
But diplomatic sources said that the parties were still meeting, and both sides have now denied the reports.