U.S. intelligence "did not see anything that suggested an attack of this type was going to unfold" in Israel, national security adviser Jake Sullivan said Tuesday.

Sullivan wouldn't tell reporters if President Joe Biden and Israeli Prime Minister Benjamin Netanyahu discussed on their Tuesday call the possibility of an Israeli ground incursion into Gaza, and how that might affect American hostages.

Sullivan did defend Israel's targeting of Hamas sites in Gaza after being asked how long the U.S. would support the airstrikes, saying this is "not retaliation," but instead it’s "Israel standing up to defend itself.”

Sullivan also said that "at this point" there is no plan for the U.S. to put American troops on the ground to help Israel.

He added, "The president was very clear today that we will be making a request to the Congress, and it will include a request for funding for support to Israel. And he has also been equally clear that we are going to renew our request to the Congress for aid to Ukraine."

-ABC News' Justin Gomez

Israeli Prime Minister Benjamin Netanyahu said, in his conversation with President Joe Biden on Tuesday, he called Hamas' attack on Israel "barbarism that has not been seen since the Holocaust."

"Hundreds of people were slaughtered," including soldiers whose heads were cut off, Netanyahu said.

"Entire families were murdered in their beds and homes, women were brutally raped and murdered, [and] more than a hundred were kidnapped, including children," he said.

Netanyahu said he told Biden that "Hamas is worse than ISIS -- and that they should be treated that way."

Minister of Defense Yoav Gallant said Israeli soldiers have gained control of Israel's southern border "and are now moving on to a full-scale response."

"Anyone who decapitates citizens, or murders women and Holocaust survivors, will be eliminated. We will use all our force," Gallant said.

To the soldiers, Gallant said, "We have full confidence in you. It is thanks to the IDF that Israel exists."

The IDF said Israeli soldiers exchanged gunfire with terrorists in the Ashkelon industrial area in the last hour, killing at least three terrorists.

-ABC News' Will Gretsky

The United States is tracking about 20 Americans who are still missing in Israel, State Department spokesperson Matt Miller said Tuesday.

Miller said that doesn't necessarily mean they are being held by Hamas.

Secretary of State Antony Blinken will visit Israel this week to work with Israeli partners directly to determine "how we can continue to best support them," Miller said.

Blinken will most likely leave on Wednesday to arrive in Israel on Thursday, he said.

Biden has not spoken with the families of the 14 Americans killed in Israel, but the State Department has been in constant contact with their families, national security adviser Jake Sullivan said Tuesday.

"The president has been making this his highest priority as he receives briefings each day about what we are doing to try to determine both what’s happening with the missing and also to ensure that we can secure the bodies of those that have perished and ensure that they get returned to their loved ones," he said.

-ABC News' Shannon Crawford and Mary Bruce

American Airlines said it will suspend flights to and from Tel Aviv through Dec. 4.

Delta suspended flights to and from Tel Aviv until the end of October, while United said its flights to and from Tel Aviv are suspended "until conditions allow them to resume."

Six people were killed and dozens were injured when a Gaza school sheltering refugees was hit by Israeli airstrikes, the United Nations Relief and Works Agency said.

At least 4,000 people have taken refuge in the school, UNRWA said.