TEL AVIV — Israel has "resumed combat in full force" against Hamas in the Gaza Strip, Prime Minister Benjamin Netanyahu said on Tuesday night.

In a defiant video statement, he warned that "negotiations will continue only under fire" and that "this is just the beginning".

His comments came after Israeli aircraft launched massive airstrikes against what the military said were Hamas targets in Gaza.

More than 400 people have been killed in the attacks, the Hamas-run health ministry said, and hundreds more injured.

The wave of strikes was the heaviest since a ceasefire began on 19 January.

The fragile truce had mostly held until now, but this new wave of attacks suggests plans for a permanent end to the war may be off the table.

The airstrikes that hit Beit Lahia, Rafah, Nuseirat and Al-Mawasi on Tuesday shattered the relative peace that Gazans had been experiencing since January, and hospitals are once again overrun with casualties.

The attacks on Gaza have been condemned by Egypt, a mediator in the talks.

The air strikes are "a blatant violation" of the ceasefire agreement and represent "a dangerous escalation", said Tamim Khallaf, the spokesman for the country's Ministry of Foreign Affairs.

"I was shocked that the war started again, but at the same time, this is what we expect from the Israelis," Hael a resident from Jabalia al-Balad told BBC Arabic.

"As a citizen, I'm exhausted. We've had enough — a year-and-a-half to this! It's enough," he added.

Key Hamas figures were killed in the airstrikes, including Major General Mahmoud Abu Watfa, deputy interior minister in Gaza and the highest-ranking Hamas security official.

In his address, Netanyahu said Israel had tried to negotiate with Hamas to release the Israeli hostages still being held in Gaza. He accused Hamas of rejecting the proposals every time.

Israel and Hamas have disagreed on how to take the ceasefire deal forward since the first phase expired in early March, after numerous exchanges of Israeli hostages and Palestinian prisoners.

The deal involves three stages, and negotiations on the second stage were meant to have started six weeks ago — but this did not happen.

Instead, the agreement was thrown into uncertainty when the US and Israel wanted to change the terms of the deal, to extend stage one which would see more hostages released.

That would have delayed the start of phase two, which was meant to establish a permanent ceasefire and required Israeli troops to pull out of Gaza.

But Hamas rejected this proposed change to the agreement brokered by US, Qatari and Egyptian mediators, calling it unacceptable. — BBC