"This decision was not taken lightly", according to a State Department statement on Thursday. "This decision was not taken lightly, and reflects USA concerns with mounting arrears at UNESCO, the need for fundamental reform in the organization, and continuing anti-Israel bias at UNESCO", State Department spokesperson Heather Nauert said in a statement on Thursday, adding that the decision would take effect on December 31, 2018.
A Downing Street spokesman said: "The Government is committed to continued United Kingdom membership of Unesco and to working with other member states in support of its important work". The withdrawal goes into effect at the end of 2018.
The outgoing UNESCO director-general, Irina Bokova, expressed her "profound regret" at the USA decision and tried to defend the reputation of the U.N. Educational, Scientific and Cultural Organization, best known for its World Heritage program to protect cultural sites and traditions.
She recalled that in 2011, after the suspension of Washington's financial participation in the organization, she said that "UNESCO has never been more important to the United States, and the United States has never been so important to UNESCO".
"Universality is critical to UNESCO's mission to strengthen worldwide peace and security in the face of hatred and violence, to defend human rights and dignity", she added, noting that UNESCO would continue to build a more just, peaceful, equitable 21st century.
It's not the first time the USA has pulled out of UNESCO: Washington did the same thing in the 1980s because it viewed the agency as mismanaged, corrupt and used to advance Soviet interests.
"The US relationship with Unesco is a matter for them".
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The US stopped paying dues to the global body in late 2011 after the agency voted to accept a Palestinian bid for full membership and now owes approximately $550 million, a State Department spokesperson said.
"Universality is critical to UNESCO's mission to strengthen worldwide peace and security in the face of hatred and violence, to defend human rights and dignity", she wrote. "It's very, very regrettable".
UNESCO's executive board plans to select her successor Friday in a secret ballot.
"UNESCO will continue to work for the universality of this Organization, for the values we share, for the objectives we hold in common, to strengthen a more effective multilateral order and a more peaceful, more just world", Bokova concluded.
Ms Bokova defended Unesco's reputation, noting its efforts to support Holocaust education and train teachers to fight anti-Semitism.
Analysts said that actually withdrawing from the organization was a significant escalation by the United States in its criticism of United Nations bodies. Permanent Representative to the UN Nikki Haley has repeatedly denounced these actions, and said the USA was "evaluating" whether or not it should continue as a member of the organization. The department also voiced concerns about an anti-Israel bias at UNESCO.
And past year, Israel suspended cooperation with it after the agency adopted a controversial resolution which made no reference to Jewish ties to a key holy site in Jerusalem.
The United Nation's education, cultural and scientific agency has passed several resolutions against Israel.