Senate Majority Leader Chuck Schumer on Saturday spoke with top officials from the Central Intelligence Agency and the State Department during a briefing on the situation in Israel.

Schumer's office released a statement, stating, "The enormous loss of life is gut-wrenching, and I am appalled at the viciousness of the attack by Hamas on innocent Israeli civilians. I expressed my commitment to top Biden Administration officials – and directly to Ambassador Herzog – to do all I can to deliver everything Israel requires in this time of urgent need. I will continue to receive regular briefings."

Schumer is currently overseas in China on a Congressional trip.

The statement continued, "This is one of the worst attacks Israel has ever experienced, and friends of Israel in the US and around the world must stand strongly by her. My heart goes out to those that lost loved ones."

The Federal Aviation Administration issued a statement Saturday night urging U.S. airlines and pilots to "use caution" when flying in Israeli airspace.

In a Notice to Air Missions (NOTAM), the FAA said to exercise extreme caution at all altitudes due to the "ongoing conflict situation between Israel and Gaza."

NOTAM's statement told flight crews to remain in contact with "air traffic control at all times" and to monitor for "possible airspace closures."

A music festival near Re'im, Israel, came under fire amid the Hamas attacks, a festivalgoer recounted to ABC News.

Eliav Klein said that around 5:30 a.m. local time Saturday, missiles and gunfire began to target the festival. He and others ran "in a panic," losing track of many of their friends. Some of Klein's friends are still missing, he said.

Footage captured rockets flying across the horizon, interrupting the festival.

-ABC News' Christopher Looft

A senior White House official told reporters Saturday evening that it is "too early" to know what involvement, if any, Iran had in the attacks in Israel.

"It's too early to say whether the state of Iran was directly involved or planning, supporting," the senior administration official said. "We are going to be looking at that very closely."

"That said, there's no doubt Hamas is funded, equipped, armed by Iran and others," the official added.

Several Israeli officials, including President Isaac Herzog, have claimed that Iran helped coordinate the attacks.

The White House official said President Joe Biden and the administration have been in contact with Palestinian and Israeli officials throughout the day.

"We are in deep talks with the Israelis about some of their particular needs," the official said.

-ABC News' Fritz Farrow

National Security Council spokesperson John Kirby avoided saying if the U.S. believed Israel's calls for civilians in Gaza to evacuate in the next 24 hours was possible but acknowledge that it was a "tall order" given how densely populated the area is.

"Well, I think we're going to be careful not to get into armchair quarterbacking the tactics on the ground by the IDF. What I can tell you is we understand what they're trying to do. They're trying to move civilians out of harm's way and giving them fair warning. Now, it's a tall order. It's a million people, and it's a very urban, dense environment, already a combat zone. I don't think anybody's underestimating the challenge here of affecting that evacuation," Kirby said in an interview on CNN Friday morning.

"But it's pretty clear that what they're trying to do is to the maximum extent possible avoid civilian casualties and also separate Hamas from the human shields. I mean, Hamas actually gave a counterorder telling Palestinians in Gaza to stay at home. Why? Because having human shields, they think, protects them," Kirby continued.

Asked about their efforts to secure a safe passage for civilians out of Gaza, Kirby reiterated that the U.S. is talking to Israel and Egypt but would not comment further on progress.

On the Rafah crossing specifically, Kirby said "So far it's still closed. But that doesn't mean were not going to still try as hard as we can to talk to the Israelis and Egyptians about getting it open and having some sort of safe passage out. It's important that we also continue to work to make sure that humanitarian assistance can get in. The United States has no intention of stopping our efforts to continue to deliver humanitarian assistance, but there has to be a path in, there has to be a path out."

Kirby had no update on the Americans who are believed to be held hostage in Gaza and could not confirm reports that 13 hostages have been killed by Israeli airstrikes, as Hamas has claimed.

-ABC News' Molly Nagle