National security adviser Jake Sullivan said Sunday that the U.S. has pressed Israel to distinguish between Hamas and Palestinian civilians amid growing pressure to protect civilians in Gaza as Israel expands its raids.

"We have conversations like friends do on the hard questions that I talked about before — on issues associated with humanitarian aid, on distinguishing between terrorists and innocent civilians, on how Israel's thinking through its military operation," Sullivan told "Face the Nation" in an interview. "Those conversations happen multiple times a day.

He said President Biden, Secretary of State Antony Blinken and Defense Secretary Lloyd Austin are involved in those conversations.

"We talk candidly, we talk directly, we share our views in an unvarnished way and we will continue to do that," he said. "But sitting here in public, I will just say that the United States is going to make its principles and propositions absolutely clear, including the sanctity of innocent human life, and then we will continue to provide our advice to Israel in private."

When asked whether the Israelis have told the U.S. at what point they will declare their mission against Hamas a success, Sullivan said "they have told us in broad terms that making sure that Hamas can never again threaten Israel in the way it threatened Israel before is their core strategic objective in this conflict."

"But in terms of what the specific milestones are, that is something that ultimately is up to Israel, this is their military operation, they will make that decision," he said. "And we will continue to ask the hard questions, Margaret, that we would ask of ourselves in a military operation like this. What exactly are the objectives? How are the means matched to the objectives? And how will this evolve over time? That's a conversation we've been having. It's a conversation we will continue to have in the days ahead."

Sullivan said any potential "humanitarian pause" in fighting between Israel and Hamas to get hostages out of Gaza could benefit the terrorist group.

"There are a lot of complicated realities in this. A humanitarian pause would be a good thing to get hostages out, but you can bet that Hamas will try to use that time to their advantage as well," Sullivan said.

On Tuesday, Blinken told the U.N. Security Council that humanitarian pauses in the conflict "must be considered" to allow food, water and medicine into Gaza, and for civilians to get out of harm's way. But the Biden administration has not supported a longer cease-fire, saying that could allow for Hamas to reposition.

Sullivan on Sunday declined to put a timeframe on how long it would take to move all hostages to safety if they were released.

"Given the number of hostages, it would be more than just hours if we're able to secure their release, and we are actively working to secure their release," he said.

Hamas has taken more than 200 hostages, according to the Israel Defense Forces, and only four have been released, including two Americans, since the Oct. 7 attack.

Meanwhile, the U.S. estimates up to 600 Americans are trapped in Gaza. Sullivan said the U.S. is in "regular contact with most of the Americans" who have been unable to leave the region.

"We can't say every single one, but all of the ones who reach out to us, we follow up with on a regular basis, even sometimes a daily basis," Sullivan said. "We know that many of them are still there, still waiting to get out. And we are working actively to try to make that happen."

Sullivan blamed Hamas for preventing foreign nationals from leaving.

"The Egyptians are prepared to let Americans and other foreign nationals out of Gaza," he said. "The Israelis have no issue with that. But Hamas is preventing their departure and making a series of demands. We're trying to work through that, to create a circumstance where all of the Americans who are in Gaza are able to get out. It is a priority for the president."

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