The Israel Defense Forces has denied accusations from the Hamas-run Gaza Health Ministry that they buried at least 283 bodies in a mass grave near Nasser Hospital in Gaza.

"The claim that the IDF buried Palestinian bodies is baseless and unfounded," the IDF said in a statement. "During the IDF’s operation in the area of Nasser Hospital, in accordance to the effort to locate hostages and missing persons, corpses buried by Palestinians in the area of Nasser Hospital were examined."

"The examination was conducted in a careful manner and exclusively in places where intelligence indicated the possible presence of hostages," the IDF said. "Bodies examined, which did not belong to Israeli hostages, were returned to their place."

White House national security communications adviser John Kirby said Tuesday that the reports of mass graves are "deeply concerning," but the White House is not in a place to validate the reports.

"I wouldn't expect a U.S. investigation," Kirby said, adding, "We'll certainly talk to our Israeli counterparts."

Israel's Ambassador to the United Nations, Gilad Erdan, is claiming that more than 2,135 workers at UNRWA, the U.N. agency for Palestinian refugees, are members of Hamas or the Palestinian Islamic Jihad.

"Hamas has infiltrated UNRWA so deeply that it is no longer possible to determine where UNRWA ends and where Hamas begins," Erdan said. "Israel calls on the donor countries to refrain from transferring their taxpayers' money to UNRWA-Gaza, as these funds will go to the Hamas terrorist organization, and that violates legislation in the donor countries themselves."

This comes after an independent review of UNRWA released on Monday found the agency had policies in place to back up its principle of neutrality, but also found UNRWA had "serious gaps in implementation," The Associated Press reported. The report made recommendations to improve the agency’s neutrality.

The report also found that Israel hadn’t provided evidence to back up its claim that a significant number of UNRWA employees were members of Hamas or PIJ, the AP said.

Iranian Foreign Ministry spokesman Nasser Kanaani called Israel’s retaliatory strike against Iran last week "harassment" that has "caused no damage whatsoever."

"In our opinion, this issue is not worthy of addressing," Kanaani said Monday.

The State Department has released its annual assessment of human rights across the globe.

The U.S. assessed that Israelis have killed or injured nearly 80,000 Palestinians in Gaza -- accounting for 3% of the population.

The State Department stressed that Israel "must conduct military operations in accordance with international law and take every feasible precaution to protect civilians."

"We continue to urgently raise concerns surrounding the deaths of and injuries to tens of thousands of Palestinian civilians in Gaza, including women, children, persons with disabilities, and other vulnerable persons," the U.S. said. "We repeatedly have pressed concerns about Palestinian civilians’ access to humanitarian assistance, displacement of the majority of the population of Gaza, and the unprecedented number of journalists killed."

The U.S. continues to review allegations that Israel violated international laws of war in Gaza and the West Bank, and part of that review will look into whether U.S. weapons were involved, Secretary of State Antony Blinken said at a news conference Monday.

Blinken said the process will be fair, whether a country is "an adversary or competitor, a friend or an ally."

-ABC News’ Chris Boccia

Hanna Siegel, niece of American hostage Keith Siegel, appeared on CBS' "Face the Nation" on Sunday morning and talked about the "surreal" feeling of seeing a recently released video purporting to show her uncle and talked about the possibility of a deal that would free him and other people thought to still be held by Hamas in Gaza.

"We've always believed that he was alive. We have to believe he's alive -- and his wife, my aunt, who was held for 52 days, [was] released in the deal that took place in November, she was with him," Siegel said. "When she came out, she told us he was alive, but this is the first time that we're seeing him, hearing him. It's surreal."

When asked about a potential hostage deal and temporary cease-fire between Israel and Hamas, Siegel said that she does think an agreement "can be reached" and pointed to an earlier deal that secured the release of her aunt and others during a brief pause in the war late last year.

Siegel also said that she believes the new release of purported hostage videos shows that Hamas is signaling they are ready to make a deal.

But she said that she is concerned that it might not be in Israeli Prime Minister Benjamin Netanyahu's "political interest to close a deal," though Netanyahu has said his goal is freeing the captives in Gaza as well as dismantling Hamas.

Siegel said that the Biden administration should "think about what they can do directly to bring our American citizens home."

She also said she has felt the "commitment from the Biden administration to get him back," referring to her uncle.

She became emotional talking about how her family missed her uncle during their Passover celebration and had a picture of him to pay tribute.

"I think there's so much swirling in the political realm that it's easy to forget that these are human beings. Keith is a grandfather, he's a husband, he's a brother, he's an uncle," she said.

She was asked whether her family is worried if a potential Israeli invasion of the Gaza city of Rafah, to further target Hamas fighters, could threaten her uncle's safety. She responded that she and her family are "very concerned."

-ABC News' Michelle Stoddart