Up to 50 Israelis who were being held hostage by Hamas have been freed, according to an Israel Defense Forces spokesperson.

They were being held in the dining hall of Kibbutz Be'eri in southern Israel, though the situation has been "neutralized," the IDF spokesperson said.

Officials still believe hostages are being held in Gaza but an exact number hasn't been released.

The FBI and the Department of Homeland Security have issued a "Public Safety Notification" to law enforcement around the U.S., urging them to remain vigilant and report any suspicious activity in the midst of the ongoing situation in Israel.

The notice says the agencies "do not currently have specific intelligence indicating a threat to the United States stemming from the Hamas attacks in Israel" but that "foreign terrorist organizations and their supporters remain committed to attacking the United States within and beyond our borders."

"In recent years, there have been several events and incidents in the United States that were purportedly motivated, at least in part, by the conflict between Israel and Hamas," the notice continued. "These have included the targeting of individuals, houses of worship, and institutions associated with the Jewish and Muslim faiths with acts of physical assault, vandalism, or harassment."

-ABC News' Mike Levine

A high-ranking Israel Defense Forces commander was killed in action Saturday, the military said.

Col. Jonathan Steinberg, 42, the commander of the Nahal Brigade, was killed during a confrontation with Hamas, IDF said.

United Hatzalah, a community-based volunteer EMS organization, said so far it has treated nearly 1,000 people for "various injuries" in southern and central Israel.

The organization said it has also transported an unspecified number of patients to hospitals in the regions via ambulance and helicopter.

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."