File Photo: The logo of the United Nations Educational, Scientific and Cultural Organization (UNESCO) is seen in front of its headquarters in Paris, France, Oct. 4, 2017. (Xinhua/REUTERS)

WASHINGTON, Oct. 12 (Xinhua) -- The United States on Thursday informed the United Nations Educational, Scientific and Cultural Organization (UNESCO) that it would formally withdraw from the organization on Dec. 31, 2018.

The decision reflected "U.S. concerns with mounting arrears at UNESCO, the need for fundamental reform in the organization, and continuing anti-Israel bias at UNESCO," U.S. State Department spokesperson Heather Nauert said in a statement.

The United States would seek to "remain engaged with UNESCO as a non-member observer state," the statement added.

The United States stopped funding UNESCO after the organization voted to include Palestine as a member in 2011. Since then, however, the United States has still maintained a UNESCO office at the organization's headquarters in Paris, France.

Meanwhile, UNESCO Director-General Irina Bokova said on Thursday that she "deeply regrets" the decision of the United States to withdraw from UNESCO.

"It's a loss to UNESCO, it's a loss to the family of the United Nations and it's a loss to multilateralism," Bokova said in a statement.