Israel-Gaza updates: Israeli forces preparing for 'wide range of offensive plans'

The FBI said it is working "aggressively" to investigate reports of Americans who have been impacted by the Hamas attacks on Israel.

"We are closely coordinating with our counterparts in the region as well as other international partners," the FBI said in a statement posted on X, the platform formerly known as Twitter, on Monday.

The statement continued: "Through our Legal Attache' office in Israel, FBI personnel are working with our partners on the ground to locate and identify any impacted Americans. Reports of deceased, injured or missing Americans are being treated with the utmost urgency and aggressively investigated. The FBI's Victim Services Division is coordinating with the Department of State to assist, as necessary, with family engagement."

The Israel Defense Forces will fight this war "as long as it takes," spokesperson Lt. Col. Res. Jonathan Conricus told ABC News in an interview on Monday.

"The goal that we have been given so far by the Israeli government is to make sure that Hamas doesn't have any military capabilities that they can use to threaten or murder Israeli citizens. That means to eradicate their ability to terrorize Israelis," Conricus said.

"That's what we've been tasked to do so far -- that may change, expand, and include political things as well as in their ability to govern, but as of now, what we're focusing on with the aerial strikes that are ongoing and the preparations of the other troops around the Gaza Strip is to strip Hamas of all of their military capabilities," he added.

The IDF is looking at "difficult and hard passes ahead," but Saturday's attack by Hamas fighters was a "watershed moment" that has fundamentally changed how the IDF responds, according to Conricus.

"Bottom line, what was true and perhaps worked for years before, won't cut the situation now and we are moving forward," he said.

In addition, 300,000 IDF reservists who were called up are "now in southern Israel," according to Conricus.

"We have mobilized our troops before -- the second Lebanon war comes to mind," he added. "But this is definitely very, very significant."

-ABC News' Matt Gutman, Ellie Kaufman and Becky Perlow

The White House released a statement shortly after President Biden spoke with key allies about the latest developments in Israel.

The leaders expressed their "steadfast and united support to the State of Israel, and our unequivocal condemnation of Hamas and its appalling acts of terrorism."

"We make clear that the terrorist actions of Hamas have no justification, no legitimacy, and must be universally condemned," the statement read.

The leaders said they will support Israel's right to defend itself.

"We further emphasize that this is not a moment for any party hostile to Israel to exploit these attacks to seek advantage," they said.

At the same time, the leaders said they "recognize the legitimate aspirations of the Palestinian people, and support equal measures of justice and freedom for Israelis and Palestinians alike."

"But make no mistake: Hamas does not represent those aspirations, and it offers nothing for the Palestinian people other than more terror and bloodshed," the statement read.

President Joe Biden will deliver remarks on the terrorist attacks in Israel from the White House at 1 p.m. ET on Tuesday, according to a White House official.

-ABC News' Justin Gomez