Since shock Hamas attacks on Israel on October 7, which left 1,400 dead, Israel has launched devastating air and ground bombardments of Gaza. The Hamas authorities say 4,385 people have died.

Israel has massed tens of thousands of troops and hundreds of tanks along the Gaza border for a widely anticipated ground invasion.

"We have to enter the next phase of the war in the best conditions, not according to what anyone tells us," military spokesman Admiral Daniel Hagari told a press conference.

"From today, we are increasing the strikes and minimising the danger.

"We will increase the attacks and therefore I called on Gaza City residents to continue moving south for their safety," Hagari added.

Israel has warned more than one million residents of a northern zone around Gaza City to flee to southern Gaza. Israel believes that Hamas leaders and infrastructure are concentrated in the north. But hundreds of thousands of civilians are said to remain in and around Gaza City.

The comments came hours after the first international aid to reach Gaza since October 7 crossed the border from Egypt.

In Israel, commanders visited frontline units on Saturday in a new sign of military readiness.

"We will enter Gaza," chief of staff Lieutenant General Herzi Halevi told one infantry brigade on a visit.

"Gaza is densely populated, the enemy is preparing a lot of things there -- but we are also preparing for them," Halevi said.

"We will enter for an operational mission, a professional one, to destroy Hamas activists, Hamas infrastructure. And we'll also keep in our minds the memory of the pictures and images and the dead from Saturday two weeks ago (October 7)," he added.