Israel has opened a new phase in its war on Hamas by expanding ground operations inside Gaza, but analysts warn the campaign is its riskiest in half a century with fallout threatening the whole Middle East.

Thousands of civilians have already died in Gaza and Israel since Hamas launched its shock 7 October attacks. And the United Nations has led warnings that thousands more will die as Israel sends troops and tanks farther into Gaza.

That adds to Western fears that Iran-backed Hezbollah could open a new front on the Lebanese border. Officials say Israel does not want to stay in Gaza and there are also concerns over who will administer the territory and pay for its reconstruction after the guns fall silent.

With Gaza's hospitals and food supplies devastated Israel's Arab neighbors worry that the images of Palestinian suffering could trigger a pro-Hamas backlash in their own countries.

Israel's Prime Minister Benjamin Netanyahu vowed an "iron fist" treatment of Hamas after its fighters attacked communities across southern Israel. They killed 1,400 men, women, and children, and took back at least 230 hostages, according to Israel.

Hamas authorities say more than 8,000 people, half of whom are children, have died in thousands of Israeli air strikes since the start of the war.

Images of the devastation have fuelled anger in many countries. Now tens of thousands of Israeli soldiers are waiting on the border for the toughest stage of a war that Netanyahu warned would be long and difficult.

"We are going to see a lot of carnage, we are going to see a lot of horrible things," said Edward Djerejian, a former US assistant secretary of state and ambassador to Israel, who bemoaned the lack of a political initiative to end the crisis.

This showdown is Israel's most perilous since the 1973 Arab-Israel war, when it was also taken by surprise, according to Jonathan Rynhold, a specialist on the Israel-Palestinian conflict at Bar-Ilan University near Tel Aviv.

Israel's 'critical moment'