Israel strikes in Gaza kill 400 Palestinian health authorities say

Israeli airstrikes pounded Gaza, killing 400 people, Palestinian health authorities said on Tuesday, collapsing a two-month ceasefire with Hamas as Israel vowed to use force to free its remaining hostages in the strip.

Israel's prime minister, Benjamin Netanyahu, said he had instructed the military to take "strong action" against the Palestinian militant group Hamas in Gaza in response to the group's refusal to release hostages held there and rejection of ceasefire proposals.

"Israel will, from now on, act against Hamas with increasing military strength," his office said in a statement.

Hamas accused Israel of overturning the hard-fought ceasefire deal agreed in January, leaving the fate of 59 hostages still held in Gaza uncertain.

Strikes in Gaza were reported in multiple locations. Officials from Gaza's Hamas-run health ministry said many of the dead were children.

In hospitals strained by 15 months of bombardment, piles of bodies in white plastic sheets smeared with blood could be seen stacked up as casualties were brought in.

The Israeli military said it hit 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 United Nations' Humanitarian Coordinator for the Occupied Palestinian Territory urged for the ceasefire in Gaza to be immediately reinstated.

"Waves of airstrikes occurred across the Gaza strip since the early hours of the morning ... This is unconscionable," Muhannad Hadi said in a statement.

Israeli media said Israel was opening shelters in multiple areas in commercial hub Tel Aviv to prepare for possible retaliation from Hamas or Yemen.

Israel's renewed intense pressure on Hamas came as tensions flared elsewhere in the Middle East, which has seen the Gaza war spread to Lebanon, Yemen and Iraq.