The relative calm of a cease-fire between Israel and Hamas came to an abrupt end on Tuesday when Israel unleashed intense strikes on the Gaza Strip, killing at least 400 people, Palestinian authorities said, threatening a collapse of the truce as Israel vowed to use force to free hostages.

Hamas, on Tuesday, confirmed that the head of its government in the Gaza Strip, Essam al-Dalis, was among those killed in Israeli strikes on the enclave.

It further said that Mahmoud Abu Watfa, the interior ministry head, and Bahjat Abu Sultan, director-general of the internal security service, were also killed in the strikes.

The surprise operation during the Muslim holy month of Ramadan raised the prospect of a full return to fighting in the 17-month conflict that has killed 48,000 Palestinians and caused widespread destruction and a humanitarian crisis across Gaza.

China on Tuesday called for steps to prevent a "humanitarian disaster" there.

"China is highly concerned about the current situation between Israel and Palestine," Foreign Ministry spokeswoman Mao Ning said, calling for parties to "avoid any actions that could lead to an escalation of the situation and prevent a larger-scale humanitarian disaster".

The United Nations' humanitarian coordinator for the occupied Palestinian territory, Muhannad Hadi, said: "This is unconscionable. A cease-fire must be reinstated immediately. People in Gaza have endured unimaginable suffering."

However, Israel's state-owned Army Radio said the move indicated the truce "has collapsed".Defense Minister Israel Katz said the operation would "continue as long as necessary" and might expand beyond airstrikes.

Israeli Prime Minister Benjamin Netanyahu said he had ordered the strikes because of a lack of progress in the ongoing talks in Qatar to extend the truce. "Israel will, from now on, act against Hamas with increasing military strength," his office said.

Hamas warned that Israel's move has put the fate of Israeli hostages in jeopardy. However, there were no reports of any attacks by Hamas several hours after the bombardment.

"Netanyahu's decision to resume war is a decision to sacrifice the occupation's prisoners and impose a death sentence on them," senior Hamas official Izzat al-Risheq said, accusing the Israeli leader of using the conflict as a political "lifeboat "to distract from internal crises.

'Shocked, angry'

Meanwhile, the main group representing hostages' families accused the government of backing out of the truce, saying it chose to give up on them. "We are shocked, angry and terrified by the deliberate dismantling of the process to return our loved ones," the Hostages and Missing Families Forum said in a statement on X.

Strikes were reported in multiple locations across Gaza. Gaza's Health Ministry said at least 413 people were killed in the strikes and hundreds more wounded. Rescuers were still searching the rubble for the dead and wounded as the strikes continued. It was among the deadliest days of the conflict.

Ramez Alammarin, 25, described carrying children to a hospital southeast of Gaza City.

" (Israel) unleashed the fire of hell again on Gaza," he told AFP, adding that bodies and limbs are on the ground. "They bombed a building in the area and there are still martyrs and wounded under the rubble… fear and terror. Death is better than life."

The United States said it had been consulted before the attacks and voiced support for Israel.

"As President (Donald) Trump has made it clear, Hamas, the Houthis, Iran, all those who seek to terrorize not just Israel, but also the US, will see a price to pay — all hell will break loose," White House Press Secretary Karoline Leavitt said in an interview with Fox News.

Tensions also flared elsewhere in the Middle East, a major supplier of oil to the global markets, which has seen the Gaza conflict spread to Yemen. In a statement, Yemen's Houthis condemned Israeli strikes on Gaza, vowing escalation in support of Palestinians, after earlier this month vowing to attack Israeli ships in the Red Sea.

Negotiating teams from Israel and Hamas had been in Doha as mediators from Egypt and Qatar sought to bridge the gap between the two sides following the end of an initial phase in the cease-fire.

With the backing of the US, Israel had been pressing for the return of hostages in exchange for a longerterm truce that would have halted fighting until after Ramadan and the Jewish Passover holiday in April.

Agencies and Xinhua contributed to this story.