As the Biden administration intensifies efforts to help American nationals leave Israel and Gaza, more than 20,000 U.S. citizens have reached out to the State Department asking for help in the wake of the Hamas attacks, including several hundred seeking to leave Gaza, according to two U.S. officials.

While not all have actively sought assistance with transportation, "many thousands" across Israel have indicated they needed help finding flights out of the country, the officials said.

Government-chartered planes have now started to ferry U.S. citizens from Israel to other countries in the region, though one official said the State Department still cannot share a detailed breakdown on the number of Americans whose departure it has already facilitated or the number of Americans still waiting for help "given this is an unfolding situation."

For Americans in Gaza, the U.S. is still eyeing the Rafah border crossing between Gaza and Egypt as a means of safe passage. Officials say they are very hopeful they will be able to work with Israel and Egypt to establish a corridor for U.S. citizens and other foreign nationals, but that it could take days to make substantial progress.

The Israeli government estimated that between 100 to 130 Americans were living in Gaza earlier this year. An official says the State Department believes hundreds more are visiting -- putting the total number in Gaza potentially between 500 and 600.

The State Department estimates that roughly 500,000 American citizens reside in Israel.

-ABC News' Shannon K. Crawford

President Joe Biden on Friday spoke briefly about his phone call with family members of missing Americans.

"We're working around the clock to secure the release of Americans held by Hamas," Biden said.

"They're going through agony not knowing what the status of their sons, daughters, husbands, wives, children are," Biden said. "It's gut-wrenching. I assured them my personal commitment to do everything possible, everything possible, to return every missing American to their families."

-ABC News' Molly Nagle

UNICEF on Friday urged Israel to rescind its call for a mass evacuation of northern Gaza, saying there needs to be an immediate humanitarian pause to "scale and sustain lifesaving services for children."

"The situation is catastrophic, with unrelenting bombing and a massive increase in the displacement of children and families. There are no safe places," UNICEF Executive Director Catherine Russell said in a statement. "An immediate ceasefire and humanitarian access are the top priorities to allow much needed aid to children and families in Gaza."

"There are rules of war," the statement continued. "Children in Gaza need lifesaving support and every minute counts.”

UNICEF said the situation is becoming "increasingly difficult and dangerous" and humanitarians have been warned to leave Gaza City, but that it will stay to provide support for children in need.

-ABC News' Ben Gittleson

Lufthansa is suspending flights to and from Beirut, Lebanon, "due to the current situation in the Middle East," the airline said in a statement on Friday.

Lufthansa and Eurowings flights to the region will be suspended through Oct. 16.

The U.S. Embassy said it'll offer transportation for Americans looking to leaving Israel beginning on Friday.

"It will take some period of time to schedule everyone seeking to depart," the embassy said. "Transportation will be by air to Athens or Frankfurt, or sea from Haifa to Cyprus. You will not be able to choose your destination – we will assign you to the next available flight or ship."

"You should be prepared to depart within 8-12 hours of receiving notice of your booking. Each traveler may bring one small carry on item no more than 22 pounds (10 kg) and one suitcase no more than 35 pounds (16 kg)," the embassy said.

Delta Air Lines said it's partnering with the government to help set up flights through Athens.

United Airlines said it's adding extra flights with capped fares between Athens and Newark, New Jersey, and will use a larger plane for its Athens to Washington flight. "We’re in close touch with the U.S. State Department as it seeks to add additional options for Americans traveling from the region," United said.

American Airlines also said it is working "closely" with the State Department on its needs.

The U.S. expects "these initial travel options to facilitate the safe departure of thousands of U.S. citizens per week," State Department spokesperson Matthew Miller said in a statement.

A separate official said that the State Department remains in contact with "several thousand" American citizens in Israel, but it’s unclear how many will ultimately decide to leave. Some have already departed.

The State Department estimates that roughly 500,000 American citizens live in Israel.

-ABC News' Amanda Maile, Will Gretsky and Shannon Crawford