Thousands of reservists have begun reporting for duty as the Israeli military presses ahead with its offensive to conquer Gaza City.
Ground forces are already pushing into the outskirts of Gaza's largest urban area, which the military has said is a stronghold of Hamas.
The city is also coming under heavy Israeli aerial and artillery bombardment, with local hospitals saying that more than 50 Palestinians have been killed there since midnight.
The military has ordered residents to evacuate and head south immediately. The UN says an estimated 20,000 have done so over the past two weeks, but almost a million remain.
UN humanitarian officials have warned that the impact of a full-blown offensive would be beyond catastrophic, not only for those in the city but for the entire Gaza Strip.
Last month, the Israel Defense Forces (IDF) said about 60,000 reservists would be called up ahead of Operation Gideon's Chariots II – the next phase of the ground offensive that it launched in May and has seen it take control of at least 75% of Gaza.
It also extended the service of 20,000 reservists who had already been mobilised.
On Tuesday, an Israeli military official said thousands had begun reporting for duty.
Israeli media said many of the reservists would be deployed to the occupied West Bank and northern Israel to free up active-duty personnel for the offensive.
They also reported that some combat units were seeing lower turnout than for previous call-ups, with reservists who had already served several tours during the 22-month war requesting exemptions for personal or financial reasons.
Prime Minister Benjamin Netanyahu announced that Israel would conquer all of Gaza after indirect talks with Hamas on a ceasefire and hostage release deal broke down in July.
At a government meeting on Sunday, he said the security cabinet had agreed the IDF's objectives were defeating Hamas and releasing all of our hostages.
The armed group is currently holding 48 hostages, 20 of whom are believed to be alive.
The hostages' families fear the new offensive will endanger them and are demanding the prime minister negotiate an agreement that would secure their release.
On the ground in Gaza on Tuesday, hospital officials said Israeli strikes and fire had killed at least 95 Palestinians since midnight.
The UN has also warned that forcing hundreds of thousands of people to move further south is a recipe for further disaster and could amount to forcible transfer, which would be a war crime.
Global food security experts have confirmed that a famine is occurring in Gaza City and projected that it will expand to the central city of Deir al-Balah and the southern city of Khan Younis by the end of September.
The situation on the ground is dire, with hospitals overwhelmed and a desperate need for medical supplies and aid.
