US 'dedicated' to helping Americans leave Gaza through Egypt amid Israel-Hamas war: Sullivan

The United States is pushing for Americans to get out of Gaza through Egypt amid the escalating Israel-Hamas war in the wake of a terror attack on Israel earlier this month, the White House's national security adviser said on Sunday.

"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.

"That has been difficult because of the ongoing operations and, frankly, because Hamas has intervened in some cases to make it hard for Palestinians, Palestinian Americans and others to be able to travel to the border crossing and get through," Sullivan said. "We're working that hard."

"Our goal is to ensure that every American who is in Gaza has safe passage out, and we will not rest until that happens," Sullivan said.

Two Americans living in Gaza told ABC News this weekend that while the State Department has been in touch with them, they have been unable to cross the Egyptian border. "It will take hours to get everyone out," one of them, Maha Barakat, said.

Early on Sunday, the U.S. Embassy in Jerusalem issued a security alert telling Americans to immediately move south if they are in the Palestinian territory that Hamas controls, ahead of an expected Israeli ground invasion of Gaza.

"U.S. citizens who can do so safely are advised to move to southern Gaza, south of Gaza Valley towards Khan Younis now," the embassy alerted early Sunday morning, adding, "We are working on potential options for departure from Gaza for U.S. citizens."

Hamas launched its attack on Israel from neighboring Gaza on Oct. 7. The militant political group has ruled the territory for approximately 16 years, leading to a blockade of the area by Israel and Egypt.

President Joe Biden, who has called on Israel to take Palestinian civilians into consideration during their retaliatory military operations, on Saturday night talked about the unfolding "humanitarian crisis" in Gaza.

"A week ago, we saw hate manifest in another way: in the worst massacre of Jewish people since the Holocaust," Biden said near the end of his speech at the Human Rights Council's national dinner, drawing a connection between the hardships faced by LGBTQ+ people and the attacks in Israel.

"More than 1,300 innocent lives lost in Israel, including at least 27 Americans. Children and grandparents alike kidnapped, held hostage by Hamas," the president said, adding, "Innocent Palestinian families -- and the vast majority of them have nothing to do with Hamas -- they're being used as human shields."

Raddatz asked Sullivan on "This Week," considering Biden's comments, whether the U.S. was satisfied with Israel's response thus far.

More than 2,300 Palestinians has been killed in Gaza, including more than 700 children, according to Palestinian officials, and there is a shortage of food and water.

"We're in touch with the United Nations to help secure the necessary supplies of food water and medicine to the citizens of Gaza, those Palestinians who have nothing to do with the barbaric terrorists who carried out this attack," Sullivan said, in part.

Pressed by Raddatz about the U.S. view of Israel's military operation, Sullivan said, "We believe in the laws of war and we believe in the full unnecessary access to humanitarian supplies. And we're going to keep working on that."

In a separate appearance on "This Week," Israel Defense Forces Lt. Col. Peter Lerner said the military's goal is to "strike Hamas from the top, through its institutions, all the way down to the individuals that conducted the butchering of our babies."

Lerner defended Israel's warnings to Gaza civilians so far, though the U.N. has criticized an Israeli order for people in the northern region of the strip to evacuate south as "impossible."

Sullivan, in his appearance, said the U.S. is also working to recover 15 Americans who are still unaccounted for.

"Do we not have any idea where they are in Gaza at this point?" Raddatz asked.

"It is a dynamic situation," Sullivan replied. "We cannot say that we have a fixed location for every American or even that we know every American who is being held."

Sullivan added: "We don't know how many of those are being held as hostages and we don't know how many of those, tragically, are deceased and their bodies have not yet been identified."

Sullivan also said that though he could not confirm the accuracy of reports that Iran sent a message through the U.N. that they would intervene if Israeli's military operations in Gaza go forward, he did say the U.S. is worried of a potential intensifying conflict along Israel's northern border with Lebanon.

"That is why President Biden has been so clear and forceful in saying that no state and no group should seek to exploit this situation to their advantage or should escalate the conflict," Sullivan said.

ABC News' Desiree Adib contributed to this report.