The number of Palestinians killed in the Israeli attack on Gaza has now surpassed 400, officials say.

Reuters - Israeli airstrikes hit Gaza, killing more than 400 people, Palestinian health officials said Tuesday, threatening the complete collapse of a two-month ceasefire, while Israel vowed to use more force to free hostages held by Hamas.

The Palestinian militant group, which still holds 59 of the approximately 250 hostages seized in its attack on Israel on October 7, 2023, accused Israel of violating the ceasefire and undermining mediators' efforts to secure a permanent truce.

Israeli Prime Minister Benjamin Netanyahu said he had instructed the military to take "strong measures" against Hamas in response to the group's refusal to release the remaining hostages and its rejection of ceasefire proposals.

Egypt, one of the mediators in the ceasefire agreement signed in January, called for restraint and urged all parties to work towards a lasting agreement.

Air strikes hit homes and tent camps from north to south of the Gaza Strip, and Israeli tanks bombarded across the border line to the east and south of the enclave.

"It was a night of hell. It felt like the first days of the war," said Rabiha Jamal, 65, a mother of five from Gaza City.

"We were getting ready to eat something before starting a new day of fasting when the building shook and the explosions began. We thought it was over, but the war has returned," she told Reuters via a messaging app.

In hospitals overwhelmed by 15 months of bombing, piles of bodies on white plastic tarps stained with blood could be seen as victims were brought in. Gaza's Hamas-run Ministry of Health reported that 404 people were killed, many of them children, and 562 people were injured.

The Israeli military said it had struck dozens of targets and that the attacks would continue for as long as necessary and extend beyond airstrikes, raising the prospect that Israeli ground troops could resume fighting.

The UN human rights chief, Volker Turk, stated that he was horrified by the Israeli bombing.

"This will add tragedy to tragedy," he said in a statement. "Israel's recourse to even more military force will only cause further torment to a Palestinian population already suffering catastrophic conditions."

Israel has halted aid deliveries to Gaza for more than two weeks, exacerbating a humanitarian crisis.

Israeli media reported that Israel was opening shelters in several areas of Tel Aviv's commercial center to prepare for possible retaliation from Hamas or Yemen.

Israel's intense and renewed pressure on Hamas comes as tensions rise in other parts of the Middle East, which has seen the Gaza war spread to Lebanon, Yemen, and Iraq.

Deadliest attack since ceasefire agreement. The attacks were far broader in scale than the regular drone strikes Israel has said it has recently carried out against suspected militants, and follow weeks of failed efforts to reach an agreement on extending the truce agreed on January 19.

Witnesses in Gaza contacted by Reuters said that Israeli tanks shelled areas in Rafah, in the southern Gaza Strip, forcing many families who had returned after the ceasefire to leave their homes again and head north to Khan Younis.

Among the dead were Mohammad Al-Jmasi, a senior member of Hamas's political bureau, and members of his family, including his grandchildren, who were at his home in Gaza City when it was hit by an airstrike, Hamas sources and relatives said. In total, at least five senior Hamas officials were killed, along with members of their families.

In Washington, a White House spokesperson said that Israel had consulted with the U.S. government before carrying out the attacks.

"Hamas could have released the hostages to extend the ceasefire, but instead chose refusal and war," declared White House spokesman Brian Hughes.

The Kremlin said on Tuesday that it was concerned about reports of "heavy civilian casualties."