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.

As time dwindles ahead of an anticipated Israeli ground invasion of Gaza, the U.S. is calling on fleeing citizens to head toward the southern border crossing to Egypt.

"We have been working around the clock. We have an entire dedicated team that is working on nothing but this: helping American citizens who are in Gaza be able to get safe passage through the border crossing to Egypt," Jake Sullivan told ABC "This Week" co-anchor Martha Raddatz on Sunday.

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.