Israel will not stop its operation in Gaza until the tunnels constructed by Hamas have been destroyed, Prime Minister Benjamin Netanyahu has said.
Speaking ahead of a cabinet meeting, he said Israel was determined to destroy the tunnels – used to attack troops and towns – “with or without a ceasefire”.
Some 425,000 people in Gaza have been displaced by fighting, the UN says.
That is as much as 25% of the population of the territory.
Israel began Operation Protective Edge on 8 July. Since then 1,390 Palestinians have been killed, most of them civilians, according to the Gaza Health Ministry.
Some 58 Israelis have been killed, of which 56 were soldiers and two civilians. A Thai worker in Israel has also died.
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.
The operation began with a focus on Hamas’ rocket-launching capability, but 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, killing a number of Israeli 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.
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.
Civilians in Gaza are braced for more strikes after a deadly day on Wednesday that saw more than 100 people die.
In the most controversial incident at least 16 people were killed when shells hit a UN-run school in the Jabaliya district of Gaza City.
The US and UN condemned the strike, with the UN secretary general saying “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.