The US is pulling out of the UN's cultural and educational organisation UNESCO, accusing it of 'anti-Israel' bias.
Anonymous officials at the US state department said the country would establish an observer mission at the Paris-based organisation to replace its representation.
UNESCO responded by saying that the withdrawal was a loss to the 'UN family' and to multi-lateralism. 'After receiving official notification by the United States Secretary of State, Mr Rex Tillerson, as UNESCO Director-General, I wish to express profound regret at the decision of the United States of America to withdraw from UNESCO,' said UNESCO director general Irina Bokova in a statement.
The agency is best known for designating world heritage sites such as Syria's Palmyra and the US Grand Canyon.
The US withdrawal from UNESCO will reportedly be effective from December 31.
The state department said in a statement: 'This decision was not taken lightly, and reflects US concerns with mounting arrears at UNESCO, the need for fundamental reform in the organization, and continuing anti-Israel bias at Unesco.'
The department added that the US would seek to 'remain engaged ... as a non-member observer state in order to contribute US views, perspectives and expertise'.
The US previously pulled out of UNESCO in the 1980s because Washington viewed it as mismanaged and used for political reasons, before rejoining it in 2003.
The agency also works to improve education for girls in poor countries, promoting, for example, better understanding of the Holocaust.
The US stopped funding UNESCO after it voted to include Palestine as a member in 2011. However, the state department has maintained a UNESCO office at its Paris headquarters, seeking to influence policies behind the scenes.