Israel launched a series of attacks against Hamas targets across the Gaza Strip early Tuesday, threatening a return to war after talks to release the remaining hostages held in the enclave stalled out.

Israeli Prime Minister Benjamin Netanyahu ordered the attacks after Hamas failed to release the hostages or accept U.S. proposals for extending a fragile cease-fire that had held for two months, his office said.

The strikes were the most extensive since the cease-fire took effect in January, taking aim at what Israel said were dozens of targets among Hamas’s leadership, mid-rank military commanders and infrastructure. Israel said the effort would continue and would expand beyond airstrikes.

“From now on, Israel will act against Hamas with increasing military force,” the prime minister’s office said.

President Trump gave Israel a green light to restart attacks on Hamas after the U.S.-designated terrorist group failed to give up hostages, an Israeli official said. Israel then gave the U.S. a heads up before starting the operation, the official said.

White House press secretary Karoline Leavitt confirmed on Fox News that Israel had given advance notice of the attacks. She warned Hamas and other regional enemies of Israel and the U.S. “will see a price to pay.”

“All hell will break loose,” she said, repeating a threat often made by Trump.

Trump has pressed for the release of all remaining hostages and has repeatedly threatened that Hamas would face a return to war if it doesn’t comply. The hostages include one remaining living U.S. citizen , dual national Edan Alexander, who was serving in the Israeli military when he was kidnapped by Hamas. Of the 59 hostages that remain in Gaza, Israel believes as many as 24 are still alive.

SENSITIVE MATERIAL. THIS IMAGE MAY OFFEND OR DISTURB Mourners gather near the bodies of Palestinians killed in Israeli strikes, at a hospital in Gaza City March 18, 2025. REUTERS/Dawoud Abu Alkas

“Hamas could have released hostages to extend the cease-fire but instead chose refusal and war,” National Security Council spokesman Brian Hughes said.

In a statement shared on Telegram, Hamas blamed Netanyahu and his government for endangering the lives of remaining hostages by overturning the cease-fire.

The fighting comes amid an upswing in violence in the Middle East after weeks of relative calm. The U.S. has launched three days of airstrikes at the Houthis, a militant group that holds much of Yemen, and Trump threatened Iran on Monday over its support for the group.

Residents reported strikes across the Gaza Strip overnight. Osama Humaid, a resident of the Al-Nuseirat refugee camp in central Gaza, said he awoke to the sound of explosions nearby.

“We were sleeping, when we heard multiple airstrikes around us at the same time,” he said. “People were screaming.”

Gaza health authorities said 44 people had been killed in the attacks as of early Tuesday, without specifying how many were combatants.

The war in Gaza began after the Hamas-led attack on southern Israel on Oct. 7, 2023, that left about 1,200 people dead and around 250 taken hostage. Israel killed Hamas’s military leadership and thousands of its fighters, but has caused widespread devastation, displacing almost all of Gaza’s roughly two million residents and rendering much of the territory uninhabitable.

Palestinian health authorities say more than 48,000 people have been killed since the war began, without specifying how many were combatants.

The Gaza cease-fire deal between Israel and Hamas had been structured in phases, calling for an initial exchange of hostages for Palestinian prisoners while deferring the more difficult question of a permanent end to the war.

The first phase of the cease-fire ended in March after Hamas returned 33 hostages, some of them dead, in exchange for the release of more than 1,700 Palestinian prisoners held in Israeli custody.

Talks to extend the cease-fire stalled, however, after Israel failed to begin talks on an end to the war and Hamas didn’t accept proposals to extend the cease-fire by releasing more of the hostages. Negotiators have continued to meet to push the talks forward.

Write to Feliz Solomon at feliz.solomon@wsj.com and Alexander Ward at alex.ward@wsj.com!