Israel 'to destroy' Hamas Gaza tunnels - Netanyahu
Israel will not stop its operation in Gaza until the tunnels constructed by Hamas militants have been destroyed, PM Benjamin Netanyahu has said.
He said he was determined to destroy the tunnels, which militants use to infiltrate Israeli territory, "with or without a ceasefire".
Some 425,000 people - about a quarter of Gaza's population - have been displaced by the fighting, the UN says.
It said the people there were "facing a precipice", and called for action.
Since Israel began its offensive in Gaza on 8 July, 1,400 Palestinians have been killed, most of them civilians, according to the Gaza Health Ministry.
It said 173 people had been killed within the past 24 hours.
Some 58 Israelis have been killed, of whom 56 were soldiers and two civilians. A Thai worker in Israel has also died.
Most of Hamas' rockets into Israel are intercepted and destroyed by Israel's Iron Dome missile defence system.
The BBC has seen evidence that appears to confirm hackers stole several secret military documents from two government-owned Israeli companies that developed the Iron Dome.
The UN has strongly condemned the continuing violence, urging both sides to agree to daily pauses in the fighting to help relief efforts.
"The reality of Gaza today is that no place is safe," UN humanitarian chief Baroness Valerie Amos told the Security Council.
The head of Unrwa, the main UN relief agency in Gaza, warned that "the population is facing a precipice".
"Should further large-scale displacement indeed occur, the occupying power (Israel), according to international humanitarian law, will have to assume direct responsibility to assist these people," Pierre Kraehenbuehl said.
Earlier on Thursday Israel called up 16,000 reservists, fuelling speculation that the ground campaign would be widened.
But the Israeli army told the BBC that the new reservists would relieve a similar number who were standing down.
The army said a total of 59,000 reservists were deployed in Gaza.
Israel's offensive, named Operation Protective Edge, began with a focus on Hamas' rocket-launching capability.
But it has since expanded to take in the threat from tunnels.
After air strikes began, the Israel Defense Forces (IDF) discovered an extensive network of tunnels leading from Gaza into Israel.
Hamas militants have launched several attacks from the tunnels, penetrating Israeli territory and killing a number of soldiers.
Reports from Israel suggest the discovery of the tunnels - and the reality that infiltrators have used them to kill Israelis inside their own country - has shocked many Israelis and bolstered support for the operation.
It launched a ground operation to destroy the tunnels on the night of 17 July, and insists that any ceasefire deal includes the right to continue that mission.
"I won't agree to any proposal that will not enable the Israeli military to complete this important task for the sake of Israel's security," Mr Netanyahu said.
The tunnels would allow Hamas to "abduct and murder civilians and IDF soldiers while simultaneously attacking from the tunnels penetrating our territory," he added.
On the ground in Gaza, Israeli shelling continued on Thursday morning, the BBC's Jon Donnison reports.
Meanwhile, a series of rocket alert sirens sounded across southern Israel. Sirens in the town of Sderot sounded several times as Mr Netanyahu spoke.
In the most controversial incident on Wednesday, at least 16 people were killed when shells hit a UN-run school in the Jabaliya district of Gaza City.
The UN said "all available evidence" suggested Israeli artillery was the cause.
Spokesman Mark Regev told the BBC that Israel would apologise if it discovered it was responsible.
"We have a policy - we don't target civilians," he said.
"It's not clear to us that it was our fire but we know for a fact there was hostile fire on our people from the vicinity of the school."
Later on Wednesday at least 17 were killed in a strike on a busy market in Shejaiya - a district already badly damaged by Israeli artillery.
Israel occupied Gaza in the 1967 Middle East war and only pulled its troops and settlers out in 2005.
Israel considered this the end of the occupation, but it still exercises control over most of Gaza's borders, water and airspace. Egypt controls Gaza's southern border.
Hamas says it will not stop fighting until a blockade, maintained by both Israel and Egypt, is lifted.