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

The World Health Organization is begging Israel to immediately reverse its evacuation order for the over 1 million living north of Wadi Gaza, saying "a mass evacuation would be disastrous for patients, health workers and other civilians left behind or caught in the mass movement."

"With ongoing airstrikes and closed borders, civilians have no safe place to go," the WHO said in a statement. "Almost half of the population of Gaza is under 18 years of age. With dwindling supplies of safe food, clean water, health services, and without adequate shelter, children and adults, including the elderly, will all be at heightened risk of disease."

"Of the thousands of patients with injuries and other conditions receiving care in hospitals, there are hundreds that are severely wounded and over 100 who require critical care," the WHO said. "Many thousands more, also with wounds or other health needs, cannot access any kind of care. The compressed timeframe, complex transport logistics, damaged roads, and, above all, lack of supportive care during transport all add to the difficulty of moving them."