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

A 74-year-old mother who is missing in Israel fought for peace her whole life, her son told ABC News Live on Monday.

Yonatan Zeigen said he last heard from his mother, Vivian Silver, at 11:07 a.m. on Saturday morning while she was hiding in a closet as Hamas fighters entered her house.

Zeigen added that he didn't know if Israeli soldiers had been to her house yet and hadn't heard "anything concrete" about the search yet.

Zeigen talked about his mother's commitment to peace, since Silver moved to a kibbutz in Israel in the 1990s.

"She fought for equality," he said. "She's been involved with a lot of different organizations promoting peace and promoting solution for the conflict.

"Up until recently, she would drive sick Palestinians from the Gaza border to Israeli hospitals through an organization called Road to Recovery," Zeigen said.

"No, I'm primarily sad, and anxious," Zeigen said when asked if he was angry about the situation. "War is blind. You can do what you do in your life...it doesn't make you any less of a target in times of war."

-ABC News' Michelle Stoddart

Former President Barack Obama released a statement Monday evening condemning Hamas' attack on Israel over the weekend.

"All Americans should be horrified and outraged by the brazen terrorist attacks on Israel and the slaughter of innocent civilians," Obama said in his statement. "We grieve for those who died, pray for the safe return of those who’ve been held hostage, and stand squarely alongside our ally, Israel, as it dismantles Hamas."

In his first on-camera comments about Israel’s evacuation request for northern Gaza, Israeli Defense Minister Yoav Gallant urged Gaza residents to head south. He noted that Hamas will use them as "camouflage," “therefore we need to separate them."

"Those who want to save their life, please go south. We are going to destroy Hamas infrastructures, Hamas headquarters, Hamas military," he said.

Defense Secretary Lloyd Austin, who appeared at the press conference with Gallant, dodged ABC News' question about how Israel could end the Hamas terror threat without inevitably risking civilian lives. Austin called Israel's military "professional" and "disciplined."

Austin described how ISIS had also embedded themselves in civilian populations and how the anti-ISIS coalition "protected civilians and created corridors for humanitarian movement even in the midst of a pretty significant fight. So again, this is a professional force. It is well led, and I have every expectation that it will be disciplined."

Austin added, "I would tell you that in countering ISIS, I felt as if we were staring evil in the eye, it was truly evil. And what we've seen from Hamas, it takes that evil to another level."

-ABC News' Matt Seyler and Luis Martinez