The United States, a close ally and major supplier of arms to Israel, could announce new military support Sunday following the Hamas attack, Secretary of State Antony Blinken said.

"We're looking at specific additional requests that the Israelis have made. I think you're likely to hear more about that later today," Blinken told CNN.

"President (Joe) Biden's direction was to make sure that we're providing Israel everything it needs at this moment to deal with the attacks from Hamas."

The conflict's worst escalation in decades has claimed more than 600 lives on the Israeli side, the government press office said, while Gaza officials reported at least 370 deaths, with thousands more wounded on each side.

"We have reports that several Americans were killed. We're working overtime to verify that. At the same time, there are reports of missing Americans and there again, we're working to verify those reports," Blinken said.

He told ABC that "this is a massive terrorist attack that is gunning down Israeli civilians in their towns, in their homes, and as we've seen so graphically, literally dragging people across the border with Gaza.

"So, you can imagine the impact this is having throughout Israel. And the world should be revolted at what it has seen."