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.

The Israel Defense Forces said Tuesday that it's "preparing to implement a wide range of offensive plans" after mobilizing hundreds of thousands of reserves and several days of combat.

In Gaza, at least 3,000 people have been killed, including about 1,000 women and 1,000 children, according to the Palestinian Ministry of Health.

Another 12,500 people in Gaza have been injured.

French President Emmanuel Macron said there's been contact with Hamas via "several friendly intermediary powers" to try and negotiate the release of hostages.

Turkey's Minister of Foreign Affairs, Hakan Fidan, said it's launched talks with Hamas' political wing as it efforts the release of foreigners, civilians and children.

National Security Council spokesperson John Kirby avoided saying if the U.S. believed Israel's calls for civilians in Gaza to evacuate in the next 24 hours was possible but acknowledge that it was a "tall order" given how densely populated the area is.

"Well, I think we're going to be careful not to get into armchair quarterbacking the tactics on the ground by the IDF. What I can tell you is we understand what they're trying to do. They're trying to move civilians out of harm's way and giving them fair warning. Now, it's a tall order. It's a million people, and it's a very urban, dense environment, already a combat zone. I don't think anybody's underestimating the challenge here of affecting that evacuation," Kirby said in an interview on CNN Friday morning.

"But it's pretty clear that what they're trying to do is to the maximum extent possible avoid civilian casualties and also separate Hamas from the human shields. I mean, Hamas actually gave a counterorder telling Palestinians in Gaza to stay at home. Why? Because having human shields, they think, protects them," Kirby continued.

Asked about their efforts to secure a safe passage for civilians out of Gaza, Kirby reiterated that the U.S. is talking to Israel and Egypt but would not comment further on progress.

On the Rafah crossing specifically, Kirby said "So far it's still closed. But that doesn't mean were not going to still try as hard as we can to talk to the Israelis and Egyptians about getting it open and having some sort of safe passage out. It's important that we also continue to work to make sure that humanitarian assistance can get in. The United States has no intention of stopping our efforts to continue to deliver humanitarian assistance, but there has to be a path in, there has to be a path out."

Kirby had no update on the Americans who are believed to be held hostage in Gaza and could not confirm reports that 13 hostages have been killed by Israeli airstrikes, as Hamas has claimed.

-ABC News' Molly Nagle