Dozens of Israeli fighter jets have struck several targets in the Al Forqan area of the Gaza Strip, which serves as a hub for Hamas, the Israel Defense Forces said. Massive blasts were seen igniting over the area at the same time.

Many of the operations against Israel this weekend were launched from the Al Forqan area, the IDF said.

-ABC News' Jordana Miller

Lt. Col. Jonathan Conricus, spokesperson for the Israel Defense Forces, called Hamas' attack "unprecedented," and said the assault will be "followed by an unprecedented Israeli response."

"I could not imagine at that time [when the incursion began Saturday] that Hamas would have the audacity … to do what they have done," he told ABC News Monday. "To launch such an unprecedented, brutal, merciless attack on Israeli citizens. … And cause the amount of casualties that Israel has never experienced ever in its history."

In Israel, at least 700 people have died and more than 2,300 others have been injured since Saturday.

The Israel Defense Forces has since launched retaliatory airstrikes on Gaza. At least 560 people have died and another 2,900 have been injured in Gaza since Saturday, Palestinian authorities said.

The IDF said it's struck 130 targets in the last three hours.

Personnel at the U.S. Embassy in Israel are now under a curfew from 8 p.m. to 6 a.m. and "are urged to stay as close to home as possible outside the curfew hours," the U.S. Embassy said in a new alert.

In addition to a ban on personal travel to Gaza and the surrounding areas, the new alert said all U.S. government personnel are also prohibited from personal travel to the West Bank.

"U.S. citizens in Israel who have family members missing in the Gaza periphery can go to the Israel National Police’s combined assistance center at 4 HaNegev Street in Airport City," the alert said.

-ABC News' Shannon Crawford

Israel Defense Forces' helicopter gunships are attacking Lebanese territory on Monday after the IDF said two rockets were fired from Lebanon.

The Lebanese army said, "The outskirts of the towns of Al-Dhaira and Aita Al-Shaab and other border areas are being subjected to air and artillery bombardment by the Israeli enemy. The Army Command calls on citizens to take the utmost precaution and caution and not to go to areas adjacent to the border in order to preserve their safety."

Of the two rockets fired from Lebanon toward Israel, one of the rockets fell in Lebanese territory and no injuries were reported.

Seventeen Americans are missing, including an unknown number of Americans being held hostage by Hamas, National Security Council spokesman John Kirby said.

"I think we all need to steel ourselves for the very distinct possibility that these numbers will keep increasing and that we may, in fact, find out that more Americans are part of the hostage pool," Kirby said.

He said the conditions and whereabouts of the hostages are not known.

"We don't know where they are, we don’t know if they're all in one group, or broken up into several groups. We don't know if they're being moved, and with what frequency and to what locations. All of those questions we're working hard to answer," he said.

Pressed by ABC News if U.S. officials have seen any proof of life, Kirby said, "I am not aware of any specific proof of live on any individual hostage."

6:09

Blinken heads to Israel to reiterate support amid conflict in Gaza

Asked if the U.S. has had any communication with Hamas, directly or through allies, Kirby said, "We're in discussions not only with the Israelis about what hostage recovery can look like, but with other allies and partners in the region. And there are some countries like Qatar that have open lines of communication with Hamas. So, of course, we're casting the net wide."

"We haven't made any policy options or operational decisions with respect to hostage recovery at this time," he said.

Kirby said there is no "specific evidence that Iran was directly involved with these specific sets of attacks" on Israel, but he added, "We are going to keep looking at it -- the book is not closed."

In recent days, the White House has consistently said there was no evidence pointing to Iran’s participation but said Iran was broadly complicit with their past funding and support for Hamas.

-ABC News' Mary Bruce