The Israeli military says it has begun the "preliminary actions" of a planned ground offensive to capture and occupy all of Gaza City and already has a hold on its outskirts.

A military spokesman said troops were already operating in the Zeitoun and Jabalia areas to lay the groundwork for the offensive, which Defence Minister Israel Katz approved on Tuesday and which will be put to the security cabinet later this week.

About 60,000 reservists are being called up for the beginning of September to free up active-duty personnel for the operation.

Hamas has accused Israel of obstructing a ceasefire deal in favour of continuing a "brutal war against innocent civilians", Reuters news agency reported.

Hundreds of thousands of Palestinians in Gaza City are expected to be ordered to evacuate and head to shelters in southern Gaza as preparations for Israel's takeover plan get underway.

Many of Israel's allies have condemned its plan, with French President Emmanuel Macron warning on Wednesday that it "can only lead to disaster for both peoples and risks plunging the entire region into a cycle of permanent war".

The International Committee of the Red Cross (ICRC), meanwhile, said further displacement and an intensification of hostilities "risk worsening an already catastrophic situation" for Gaza's 2.1 million population.

Israel's government announced its intention to conquer the entire Gaza Strip after indirect talks with Hamas on a ceasefire and hostage release deal broke down last month.

Speaking at a televised briefing on Wednesday, Israel Defence Forces (IDF) spokesperson Brigadier General Effie Defrin said Hamas was "battered and bruised" after 22 months of war.

"We will deepen the damage to Hamas in Gaza City, a stronghold of governmental and military terror for the terrorist organisation," he added. "We will deepen the damage to the terror infrastructure above and below the ground and sever the population's dependence on Hamas."

But Defrin said the IDF was "not waiting" to begin the operation.

"We have begun the preliminary actions, and already now, IDF troops are holding the outskirts of Gaza City."

Two brigades were operating on the ground in the Zeitoun neighbourhood, where in recent days they had located an underground tunnel that contained weapons, and a third brigade was operating in the Jabalia area, he added.

In order to "minimise harm to civilians," he said, Gaza City's civilian population would be warned to evacuate for their safety.

A spokesman for Gaza's Hamas-run Civil Defence agency, Mahmoud Bassal, told AFP news agency on Tuesday that the situation was "very dangerous and unbearable" in the city's Zeitoun and Sabra neighbourhoods.

The agency reported that Israeli strikes and fire had killed 25 people across the territory on Wednesday. They included three children and their parents whose home in the Badr area of Shati refugee camp, west of Gaza City, was bombed, it said.

Defrin said the IDF was also doing everything possible to prevent harm to the 50 hostages still being held by Hamas in Gaza, 20 of whom are believed to be alive. Their families have expressed fears that those in Gaza City could be endangered by a ground offensive.

The ICRC warned of a catastrophic situation for both Palestinian civilians and the hostages if military activity in Gaza intensified.

"After months of relentless hostilities and repeated displacement, the people in Gaza are utterly exhausted. What they need is not more pressure, but relief. Not more fear, but a chance to breathe. They must have access to the essentials to live in dignity: food, medical and hygiene supplies, clean water, and safe shelter," a statement said.

"Any further intensification of military operations will only deepen the suffering, tear more families apart, and threaten an irreversible humanitarian crisis. The lives of hostages may also be put at risk," it added.

It called for an immediate ceasefire and the rapid and unimpeded passage of humanitarian assistance across Gaza.

Mediators Qatar and Egypt are trying to secure a ceasefire deal and have presented a new proposal for a 60-day truce and the release of around half of the hostages, which Hamas said it had accepted on Monday.

Israel has not yet submitted a formal response, but Israeli officials insisted on Tuesday that they would no longer accept a partial deal and demanded a comprehensive one that would see all the hostages released.

On Wednesday, Hamas accused Israeli Prime Minister Benjamin Netanyahu of disregarding the mediators' ceasefire proposal and said he was the "real obstructionist of any agreement", according to a statement cited by Reuters.

The Israeli military launched a campaign in Gaza in response to the Hamas-led attack on southern Israel on 7 October 2023, in which about 1,200 people were killed and 251 others were taken hostage.

At least 62,122 people have been killed in Gaza since then, according to the territory's health ministry. The ministry's figures are quoted by the UN and others as the most reliable source of statistics available on casualties.