A weapon used in a strike on a UNRWA school sheltering displaced people on June 6 appears to be U.S.-made, three munitions experts told ABC News.

Journalist Emad Abu Shawiesh captured video of weapons fragments at the UNRWA al Sardi school building in Nuseirat in Gaza on June 6.

The weapon fragments seen in the video are consistent with the nose section of a U.S.-made GBU-39 "Small Diameter Bomb," Trevor Ball, a former U.S. Army explosive ordinance disposal specialist, told ABC News.

The GBU-39 also appeared to have been employed in a deadly strike on May 26 in Rafah, Gaza, according to Ball and another munitions expert, who asked not to be named due to the sensitivity of the issue.

Mark Hiznay, an associate director with the Crisis, Conflict and Arms Division of Human Rights Watch, told ABC News the image shows the remnants of a GBU-39.

N.R. Jenzen-Jones, a director at the consultancy Armament Research Services, said the image was consistent with the Small Diameter Bomb series.

“Given what we know about the IDF arsenal and munitions used in previous strikes, the remnants are most likely from a GBU-39 SDB and include a portion of the nose (forward section) of the bomb,” Jenzen-Jones said, adding that other munitions could have been used in the strike, which he had not yet assessed in detail.

-ABC News Chris Looft

The U.S. State Department has sanctioned a militant Palestinian group operating in the West Bank known as "Lions’ Den," it announced Thursday.

The department said the group claimed responsibility for several drive-by shootings around Nablus in 2022, injured and killed Palestinian civilians during clashes with Palestinian Authority Security forces that same year, and that its fighters reportedly targeted Israeli forces at a checkpoint this past April.

The Lions’ Den was the target of an Israeli raid in February. The group has been blamed for much of the surging violence in the West Bank during recent months.

"The United States condemns any and all acts of violence committed in the West Bank, whoever the perpetrators, and we will use the tools at our disposal to expose and hold accountable those who threaten peace and stability there," State Department spokesperson Matt Miller said.

The Biden administration has also imposed a number of sanctions on Israeli West Bank settlers earlier this year; targets include organizations accused of fundraising for extremist settlers and allies of Israel’s far-right National Security Minister Itamar Ben-Gvir.

-ABC News' Shannon Crawford

The United States and 16 other countries released a joint statement this morning calling on Hamas to accept a cease-fire proposal and hostage release deal outlined by President Joe Biden.

"We note that this agreement would lead to an immediate ceasefire and rehabilitation of Gaza together with security assurances for Israelis, and Palestinians, and opportunities for a more enduring long-term peace and a two-state solution," the joint statement said.

The statement was issued by leaders of the United States, Argentina, Austria, Brazil, Bulgaria, Canada, Colombia, Denmark, France, Germany, Poland, Portugal, Romania, Serbia, Spain, Thailand and the United Kingdom.

-ABC News' Justin Gomez and Kevin Shalvey

Dozens of people were killed and scores were injured in an Israeli strike on a school in Gaza, the local U.N. agency said on Thursday.

The Israel Defense Forces confirmed the airstrike, saying the school had a Hamas compound "embedded inside" of it.

"Hamas and Islamic Jihad terrorists who belonged to the Nukhba Forces and took part in the murderous attack on communities in southern Israel on October 7th were operating in the compound," IDF officials said in a statement.

The death toll was expected to be be 35 and 45 people, the U.N. Agency for Palestine Refugees said, adding that it had not yet been able to independently verify those figures.

The school in the Nuseirat area, near central Gaza, was struck overnight or early in the morning on Thursday, UNRWA said. There were possibly a few strikes, the agency said.

IDF officials said they had taken measures to "to reduce the risk of harming uninvolved civilians during the strike, including conducting aerial surveillance, and additional intelligence information."

- ABC News’ Victoria Beaule and Kevin Shalvey

The U.S. continues to push Hamas to agree to the cease-fire proposal President Joe Biden outlined Friday, saying Hamas' stated opposition to the deal has yet to be officially transmitted.

"We've seen some public comments from Hamas officials, but we have not yet gotten an official response from Hamas to the Qataris, who are the mediator to whom Israel gave their proposal that was transmitted to Hamas," White House national security adviser Jake Sullivan told ABC's George Stephanopoulos on "Good Morning America" Wednesday.

"The ball is in Hamas's court," Sullivan continued. "Israel has accepted the proposal. The world has endorsed the proposal. Now it's time for Hamas to say yes to it."

Sullivan argued the latest multi-phase proposal is key to ending the war, returning hostages, and increasing the flow of aid into Gaza, while ensuring Israel's security and a better future for Palestinians.

"That's what's on offer," Sullivan said. "That's what Hamas needs to step up and take and we're awaiting to get their official response."

Asked whether Biden thinks Israeli Prime Minister Benjamin Netanyahu was prolonging the war for political gain — which he suggested in a Time magazine interview out Tuesday — Sullivan pointed to Biden's answer to a question Tuesday evening asking if Netanyahu was playing politics.

"I don't think so. He's trying to work out the serious problem he has," Biden said Tuesday.

"And from our perspective, we're not going to delve into Israeli politics," Sullivan added. "What we're going to do is focus on the fundamental task at hand, which is President Biden's effort to end this war, get the hostages home, make sure Israel's safe and make sure the Palestinian people have a decent future."

-ABC News' Fritz Farrow