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 first U.S. charter flight to evacuate Americans from Israel has departed the country and is now en route to Europe, John Kirby, spokesperson for the National Security Council, told reporters on Friday. Kirby didn’t provide the exact destination in Europe.

He said more flights are expected to depart "in the coming days" and that "the State Department will continue to organize these charter flights for as long as there is a demand from US citizens for departure assistance."

He said the U.S. is still exploring "other options" to expand evacuation capacity, which also includes an option by sea.

Kirby also spoke to the heightened alert across the U.S.

"I want to be completely and crystal clear on one thing: At this time, none of our intelligence agencies have any specific intelligence indicating a threat to the United States stemming from the Hamas terrorist attack in Israel," Kirby stressed.

-ABC News' Justin Gomez