GAZA CITY — An Israeli strike flattened a high-rise in Gaza City on Saturday — the second in as many days — after the military warned people to move to a "humanitarian zone" ahead of a planned offensive against the urban center.

Israel has been warning for weeks of a new assault on the Palestinian territory's largest city, without issuing a timeline.

It has stepped up airstrikes and ground operations on the city's outskirts, sparking fears it could worsen the already dire conditions.

On Saturday, Israeli aircraft dropped thousands of leaflets on western neighborhoods calling on residents to evacuate, witnesses and an AFP journalist said.

Nafez Anis, who has been living in a tent with his family in Gaza City, said he had read the leaflet, but was not planning to leave.

"Where should we go?" he told AFP. "We will wait, and when we see Israeli tanks approaching here, we will leave."

Gaza civil defense agency spokesman Mahmud Bassal told AFP that 56 Palestinians had been killed by Israeli fire during the day, including 19 near an aid distribution center in the north.

The military said on Saturday that it struck a Gaza City high-rise that Hamas was using "to monitor "Israeli troops and added that it had taken "measures to mitigate harm to civilians".

Witnesses identified the building as the Sussi residential tower and said it was destroyed. Israeli Defense Minister Israel Katz shared a video showing the roughly 15-story structure collapsing in a cloud of dust and smoke.

Hamas condemned the attack and denied using residential or civilian buildings for military purposes.

Meanwhile, Israeli Foreign Minister Gideon Saar told reporters on Sunday that the conflict could end immediately if Hamas released the remaining hostages being held in Gaza and laid down its weapons.

In response, senior Hamas official Basem Naim told Reuters that it would not lay down its arms but would release all of the hostages if Israel agreed to end the conflict and withdraw its forces from Gaza.

Last month, Israel launched an assault on Gaza City and its forces are now just a few kilometers from the city center. Overnight, strikes killed 14 people across the city, health officials said, including a strike on a school sheltering displaced Palestinians.

Agencies via Xinhua