JERUSALEM/GAZA/UNITED NATIONS - Israeli Prime Minister Benjamin Netanyahu said Tuesday that Israel will escalate its renewed assault on the Gaza Strip and that "from now on, the negotiations (on Gaza ceasefire) will take place only under fire."

"We have returned to fighting with full force," Netanyahu said in a televised address. "From now on, Israel will act against Hamas with increasing intensity."

"Hamas has already felt the weight of our might in the past 24 hours," he said. "And I want to promise you, and them: this is just the beginning."

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"We will continue fighting to achieve all the war's objectives -- freeing all our hostages, eliminating Hamas, and ensuring that Gaza will no longer pose a threat to Israel," he said, adding, "We are reshaping the Middle East."

Netanyahu claimed that the overnight surprise attack was launched because Hamas rejected Israeli and US proposals to extend the first phase of the Gaza ceasefire deal that ended on March 1. The proposals demanded prolonging the first phase and Hamas freeing additional hostages.

"Military pressure is a necessary condition for the release of additional hostages," he said, dismissing media reports saying that the renewed assault was aimed at ensuring his political survival.

Earlier on Tuesday, Israeli Foreign Minister Gideon Sa'ar said Israel's renewed assault on Gaza is not "a one-day operation."

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Talking to the American Israel Public Affairs Committee, a major Washington-based pro-Israel lobbying group, in Jerusalem, Sa'ar said the initial decision to launch the attacks was made "several days ago".

He also confirmed that officials with US President Donald Trump's administration "were informed before the attacks and supported it".

According to figures released by the Israeli military, Israeli forces launched on early Tuesday about 80 airstrikes across Gaza within some 10 minutes.

The airstrikes, which have killed more than 400 people so far, have been widely condemned by the international community.

Meanwhile, Hamas announced on Tuesday evening that it remains in constant contact with mediators and is engaging responsibly and positively with all proposals aimed at halting the Israeli "aggression" against and lifting the blockade on Gaza.

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In a press statement, Hamas spokesman Abdul Latif al-Qanou said the movement has not rejected the proposal put forward by Trump's envoy to the Middle East Steve Witkoff, but has responded positively to it.

Al-Qanou accused Netanyahu of resuming the war to derail the agreement.

He said Israel has tightened its blockade by closing crossings, preventing the entry of humanitarian aid, and refusing to enter the second phase of negotiations, to overturn the agreement and escalate the conflict.

UN humanitarian chief on Tuesday urged a renewed Gaza ceasefire and called on Israel to lift the blockade of life-saving aid and commercial supplies to the enclave.