Nikki Haley, the exiting U.S. ambassador to the United Nations, issued a harsh assessment of UNESCO on Tuesday, one day after the United States and Israel officially quit the U.N. agency, alleging an anti-Israel bias.

"UNESCO is among the most corrupt and politically biased UN agencies," Haley wrote in a Twitter message. "Today the U.S. withdrawal from this cesspool became official. #USStrong"

The Trump administration filed its notice to withdraw in October 2017 from UNESCO (United Nations Educational, Scientific and Cultural Organization), and the administration of Israeli Prime Minister Benjamin Netanyahu followed suit.

CLICK HERE TO GET THE FOX NEWS APP

Paris-based UNESCO, which supports various educational and cultural projects around the world, has been denounced by critics for criticizing Israel's occupation of east Jerusalem, naming ancient Jewish sites as Palestinian heritage sites and granting full membership to Palestine in 2011.

Israeli U.N. envoy Danny Danon said Tuesday that his country "will not be a member of an organization whose goal is to deliberately act against us, and that has become a tool manipulated by Israel's enemies.

"UNESCO is a body that continually rewrites history, including by erasing the Jewish connection to Jerusalem," Danon said, according to the Jerusalem Post.

The withdrawals are mainly procedural yet deliver a new blow to UNESCO, co-founded by the U.S. after World War II to foster peace. But they will not greatly impact UNESCO financially, since it has been dealing with a funding slash ever since 2011, when both Israel and the U.S. stopped paying dues after Palestine was voted in as a member state.

Since then, officials estimate that the U.S. — which accounted for around 22 percent of the total budget — has accrued $600 million in unpaid dues, which was one of the reasons for President Trump's decision to withdraw. Israel owes an estimated $10 million.

UNESCO Director General Audrey Azoulay took up her post just after Trump announced the withdrawal.

Azoulay, who has Jewish and Moroccan heritage, spent the last year lobbying for the two countries to remain members, the Jewish Telegraphic Agency reported.

She presided over the launch of a Holocaust education website and the U.N.'s first educational guidelines on fighting anti-Semitism — initiatives that might be seen as responding to U.S. and Israeli concerns.

But Washington ignored Azoulay's efforts to get the two countries to reconsider, which included brokering compromises that saw anti-Israel resolutions delayed or softened, according to the TImes of Israel.

Officials said that many of the reasons the U.S. cited for withdrawal do not apply anymore, noting that since then, all 12 texts on the Middle East passed at UNESCO have been consensual among Israel and Arab member states.

ISRAELI AMBASSADOR TO THE UN: NIKKI HALEY HAS FOUGHT THE UN'S HYPOCRISY AND MORAL BANKRUPTCY

In recent years, Israel has been infuriated by resolutions that ignore and diminish its historical connection to the Holy Land and that have named ancient Jewish sites as Palestinian heritage sites.

The State Department couldn't comment because of the U.S. government shutdown.

Earlier, the department told UNESCO officials the U.S. intends to stay engaged at UNESCO as a non-member "observer state" on "non-politicized" issues, including the protection of World Heritage sites, advocating for press freedoms and promoting scientific collaboration and education.

The U.S. could potentially seek that status during UNESCO Executive Board meetings in April.

The Associated Press contributed to this report.