DEIR AL-BALAH, the Gaza Strip — Israel began airstrikes over the Gaza Strip early Tuesday, killing around 400 Palestinians, according to local health officials, and breaking a ceasefire in effect since January with its bloodiest shelling in a 17-month conflict with Hamas. Prime Minister Benjamin Netanyahu ordered the strikes, which killed largely women and children, after Hamas refused to modify the cease-fire deal. According to officials, the operation is ongoing and will likely grow. The White House said that it had been contacted and expressed support for Israel’s actions. The Israeli military ordered residents to evacuate eastern Gaza and travel to the territory’s center, implying that Israel may resume ground operations soon. The new push comes as humanitarian groups warn that supplies are running out

“Israel will now act against Hamas with increased military strength,” Netanyahu’s office stated. The onslaught during the Muslim holy month of Ramadan could mark the official resumption of a conflict that has already killed tens of thousands of Palestinians and inflicted enormous devastation in Gaza. It also sparked fears about the fate of Hamas’ about two dozen hostages, who are thought to be still alive.

The renewal of the campaign against Hamas, which receives support from Iran, came as the U.S. and Israel stepped up attacks this week across the region. The U.S. launched deadly strikes against Iran-allied rebels in Yemen, while Israel has targeted Iran-backed militants in Lebanon and Syria. A senior Hamas official said Netanyahu’s decision to return to war amounts to a “death sentence” for the remaining hostages. Izzat al-Risheq accused Netanyahu of launching the strikes to save his far-right governing coalition.

Hamas said at least six senior officials were killed in Tuesday’s strikes. Israel said they included the head of Hamas’ civilian government, its justice minister and two security agency chiefs. There were no reports of any attacks by Hamas several hours after the bombardment. But Yemen’s Houthi rebels fired rockets toward Israel for the first time since the ceasefire began. The volley set off sirens in Israel’s southern Negev desert but was intercepted before it reached the country’s territory, the military said. The strikes came as Netanyahu faces mounting domestic pressure, with mass protests planned over his handling of the hostage crisis and his decision to fire the head of Israel’s internal security agency. His latest testimony in a long-running corruption trial was canceled after the strikes.

The strikes appeared to give Netanyahu a political boost. A far-right party led by Itamar Ben-Gvir that had bolted the government over the ceasefire announced Tuesday it was rejoining. The main group representing families of the hostages accused the government of backing out of the ceasefire. “We are shocked, angry and terrified by the deliberate dismantling of the process to return our loved ones from the terrible captivity of Hamas,” the Hostages and Missing Families Forum said.

Instead, Israel demanded Hamas release half of the remaining hostages in return for a ceasefire extension and a vague promise to eventually negotiate a lasting truce. Hamas refused, demanding the two sides follow the original deal, which called for the halt in fighting to continue during negotiations over the second phase. The deal had largely held, though Israeli forces have killed dozens of Palestinians who the military says approached its troops or entered unauthorized areas. Egypt, Qatar and the United States have been trying to mediate the next steps. Israel says it will not end the war until it destroys Hamas’ governing and military capabilities and frees all hostages – two goals that could be incompatible.

A full resumption of the war would allow Netanyahu to avoid the tough trade-offs called for in the second phase and the thorny question of who would govern Gaza. It would also shore up his coalition, which depends on far-right lawmakers who want to depopulate Gaza and rebuild Jewish settlements there. Released hostages have repeatedly implored the government to press ahead with the ceasefire to return all remaining captives. Tens of thousands of Israelis have joined protests calling for a ceasefire and return of all hostages. ___ Federman reported from Jerusalem and Magdy from Cairo. Associated Press reporters Mohammad Jahjouh in Khan Younis, Gaza Strip; Abdel Kareem Hana in Gaza City, Gaza Strip; Fatma Khaled in Cairo; and Tia Goldenberg in Tel Aviv, Israel, contributed.