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 U.S. Embassy in Jerusalem on Sunday morning urged U.S. citizens trapped in the Gaza Strip to move to southern Gaza along the main highway, the Salah al-Din Street.

U.S. citizens who can do so safely were advised by the embassy to flee to the south of the Gaza Valley toward the city of Khan Younis as U.S. officials work on potential options for getting them out of Gaza.

As of Sunday morning, the only exit to the south of Gaza, the Rafah crossing at the Egyptian border, remained closed to all seeking to flee Gaza, officials said.

But Tala Herzallah, a Palestinian woman trapped in Gaza, told ABC News Sunday that Israel Defense Forces are continuing to bomb both Khan Younis and Rafah, saying homes were hit in the areas Saturday night.

"They’re telling us to move there, and then they are bombing the houses there without warning people," Herzallah said.

The military conflict between Israel and Hamas is ongoing, making identifying departure options for U.S. citizens complex, the U.S. Embassy said.

Embassy officials encouraged U.S. citizens to complete a crisis intake form to provide contact information "should we need to reach out to you on short notice."

-ABC News' Clark Bentson