A senior U.S. defense official called the attack in Israel “unprecedented,” saying the conflict is different than past fights between Hamas and Israel because of the “ISIS-level savagery that we have seen committed against Israeli citizens,” and the “indiscriminate violence.”

The official said the Department of Defense has expressed its “unequivocal support for Israel’s right to defend itself.” The official said the U.S. has the ability to conduct long-range strikes but declined to say whether the U.S. military could use those capabilities to strike militants trying to enter Israel or in Syria if they are supporting Hamas. “I’m not going to get into hypotheticals,” the official said.

The official said the USS Ford carrier strike group will arrive “very soon,” but declined to provide specifics. The carrier strike group is deploying to minimize the risk of wider-spread conflict and as a deterrent signal to Iran, Lebanese Hezbollah and others in the region who may be looking to expand the fighting in the region. The message is that they “should think twice and not take advantage of the instability.” 

The official said the U.S. is surging support to Israel including air defense and munitions, which includes asking U.S. industry to expedite shipments of weapons already destined for Israel and looking at what other supplies and equipment are available in U.S. stockpiles. The U.S. is also talking to Israel about its air defense needs, said the official, and the U.S. could provide the Israelis with more air defense support.

The European Union's executive leadership today said it would review its assistance to Palestinian authorities in the wake of Hamas' attack on Israel.

The review, described as urgent, was announced after Commissioner Oliver Varhelyi said earlier today all payments from the E.U.'s development program for Palestinians would be "immediately suspended." 

The European Commission, which runs the E.U.’s day-to-day affairs, subsequently said in a statement there were no immediate payments to suspend. But it said any ongoing or future support of the Palestinian Authority and the broader Palestinian population may "need to be adjusted."

"The objective of this review is to ensure that no EU funding indirectly enables any terrorist organization to carry out attacks against Israel," the commission said in the statement.

Earlier in the day, Varhelyi, citing the Hamas attack as a "turning point," said the E.U. would halt its support, said to be worth about $730 million.

He said the E.U. was "the biggest donor of the Palestinians."

Natalia Casarotti, an Israeli mother whose 21-year-old son attended the music festival where Hamas launched its attacks Saturday, pleaded for the Israeli government to bring back her son.

Casarotti told MSNBC today that she has not heard from her son since before he left for the event, but he purportedly called a friend later on Saturday to say that he had badly injured his leg.

“I want my son. I want the government to bring back my son and I want my son to come back home alive. That’s the only thing I want,” Casarotti said.

Casarotti said she has given DNA to Israeli police, but has otherwise had no contact with the government or learned any further information. She said she has avoided photos and videos online and is trying to remain “positive.”

“I really try to stay positive. People say about different videos on the media, I am against even try to check them to watch them ... I won’t watch those videos or check pictures that [are] sent from terror groups,” Casarotti said.

President Joe Biden today said at least 11 Americans are known to have been killed in Hamas' attack on Israel.

"We are seeing the immense scale and reach of this tragedy," he said in a statement this afternoon. "Sadly, we now know that at least 11 American citizens were among those killed—many of whom made a second home in Israel."

He said there is an unknown number of United States citizens missing, and that diplomatic authorities are working with Israel to track them down.

Biden said the United States believes Americans may have been kidnapped.

"While we are still working to confirm, we believe it is likely that American citizens may be among those being held by Hamas," he said. "I have directed my team to work with their Israeli counterparts on every aspect of the hostage crisis, including sharing intelligence and deploying experts from across the United States government to consult with and advise Israeli counterparts on hostage recovery efforts."

Russell Langer, from the Jewish Leadership Council, said on Sky News that on Saturday morning he received a text message from family members living near the Gaza border that said: ''We're stuck. They've come in and burned our house.''

Langer said that his aunt, her daughter and her husband, and their 10-day-old baby were inside the home in a safe room.

"When Hamas couldn't get them out [of the safe room], they set the house on fire with them inside,'' Langer told Sky News.

Langer said his aunt and her family were stuck inside the safe room for around nine hours with no access to food, water or a bathroom.

"[They were] stuck watching the fact that there were Hamas terrorists inside their house on the security footage, having to hold on to the handle to make sure that [Hamas] couldn't get in.''

Langer said that the room filled up with smoke and they had to lift the baby up to the window to breathe. After the harrowing nine hours, Langer said the Israeli army reached them, and they have been recovering in hospital for the past two days.

"They're not well, but they're recovering," said Langer.

Noa Beer had been anticipating the SuperNova X music and arts festival for months, helping organize the party in the Israeli desert. But when the day finally came, what was supposed to be a celebration of peace turned into a bloodbath. She barely escaped alive.

In the midst of Hamas’ brutal attack Saturday that killed 260 festivalgoers, Beer fled by car. At one point, she was surrounded by gunmen opening fire.

“They looked in my eyes and they saw terror,” she told NBC News by phone.

Read the full story here.

In Gaza and the West Bank, 687 people have been killed, the Palestinian Health Ministry said Monday night, local time.

John Kirby, coordinator for strategic communications on the National Security Council, said on MSNBC this afternoon that the United States will continue to back Israel in its counterattack on Hamas in the Gaza Strip.

"We know that Israel has to work to defend itself, and they're doing that aggressively right now," Kirby said. "But Israel is a great democracy, a very vibrant democracy, and we share a lot of the same values, democratic institutions and and values about innocent life. And we're going to continue to obviously, stay lashed up closely with Israeli officials as they continue to prosecute this war," he added.

Kirby also said that the U.S. is not officially aware of any Americans being taken hostage in Gaza, but that "we have to assume, sadly, that there's a strong possibility that some could be."

Ruby Chen, the father of missing IDF soldier and U.S.-Israeli dual citizen Itay Chen, said on CNN today that he does not think the United States is doing enough to locate its missing citizens.

Chen said he was notified by an IDF commander that his son was missing in action Saturday morning. He said he reached out to the U.S. Embassy in Tel Aviv but said he believes that the U.S. is taking a "back seat" in investigating what happened to his son.

"I think that the U.S., at a minimum, needs to demand that any prisoner of war be treated according to international law,'' Chen told CNN. "They should be doing much more in order to find these citizens who are missing.''

Chen said his son was hoping to come home to celebrate his brother's bar mitzvah Saturday.

"We are all praying and hoping that we will be able to celebrate this together with our family and with Itay.''