State Department spokeswoman Heather Nauert said Washington would establish an "observer mission" to replace its representation at the Paris-based agency.
Hours later, Israeli Prime Minister Benjamin Netanyahu said Israel would quit too, calling the US decision "brave and moral".
"The prime minister instructed the foreign ministry to prepare Israel's withdrawal from the organisation alongside the United States," Netanyahu's office said in a statement.
The United States was angered in 2011 when UNESCO members granted Palestine full membership of the body, despite opposition from its ally Israel. The move resulted in both the US and Israel to halt their contributions to the agency.
Washington opposes any move by UN bodies to recognise the Palestinians as a state, believing that this must await a negotiated Middle East peace deal.
But US President Donald Trump's administration is also reviewing many of its multilateral commitments, pursuing what he calls an "America First" foreign policy.
Nauert said the State Department had notified UNESCO's outgoing Director-General Irina Bokova of their decision earlier Thursday.
"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," she said in a statement.
"The United States indicated to the director-general its desire to remain engaged with UNESCO as a non-member observer state in order to contribute US views, perspectives and expertise on some of the important issues undertaken by the organization, including the protection of world heritage, advocating for press freedoms and promoting scientific collaboration and education."
The news of Washington’s decision comes as members of the UNESCO executive board are in the midst of nominating a successor for Bokova.
'We need the United States'
Source : http://www.france24.com/en/20171012-us-withdraws-unesco-amid-palestinian-tensions