JERUSALEM -- 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."

"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."

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.