The Israeli military has begun a ground offensive against Palestinian militants in the Gaza Strip, extending its 10-day-old Operation Protective Edge.
It said it was in response to continued militant rocket fire and to strike a “significant blow to Hamas”, which controls Gaza.
Hamas said Israel would pay a high price for the ground offensive.
There had been a five-hour humanitarian truce on Thursday, but exchanges of fire resumed when it ended.
Some 230 Palestinians and one Israeli have died during the Operation Protective Edge period.
In a statement, the Israel Defense Forces said: “Following 10 days of Hamas attacks by land, air and sea, and after repeated rejections of offers to de-escalate the situation, the IDF has initiated a ground operation within the Gaza Strip.”
It said the goal was to “establish a reality in which Israeli residents can live in safety and security without continuous indiscriminate terror, while striking a significant blow to Hamas’ terror infrastructure”.
One Hamas spokesman told Reuters news agency the ground offensive was “foolish” and would have “dreadful consequences”.
The Palestinian Maan news agency said an intensive bombardment of Gaza by Israeli planes, artillery and ships was under way.
The BBC’s Quentin Sommerville in Tel Aviv says media colleagues in Gaza have reported seeing Israeli commandos on the beach there.
Israeli media said one key aim of the ground offensive was to destroy militant tunnels that could be used to infiltrate militants into Israel.
Israel says it has carried out more than 1,960 attacks on Gaza since 8 July, while militants have fired some 1,380 rockets at Israel.
The UN says at least 1,370 homes have been destroyed in Gaza and more than 18,000 people displaced in recent hostilities.
It says most of those killed in Gaza have been civilians.
The ground offensive follows attempts in Cairo to negotiate a new ceasefire.
Egypt has been mediating the negotiations between Israel and Hamas.
There had been some reports that a new truce would start at 06:00 local time (03:00 GMT) on Friday.
However, both Israel and Hamas later dismissed the reports.
Thursday’s temporary ceasefire had been requested by the UN and other international organisations to provide emergency relief and distribute water, food and hygiene kits to the people of Gaza.
The truce lasted from 10:00 and 15:00 local time, although both sides reported violations.
But almost immediately after it ended, Israel reported renewed militant rocket fire and there were fresh air strikes on targets in Gaza.
The health ministry in Gaza said one Israeli air strike had hit a home in the Sabra area of Gaza City, killing three children – aged between seven and 10 – from the same family.