The United States on Tuesday announced it has left UNESCO, saying the UN cultural and education agency, best known for establishing world heritage sites, is biased against Israel and promotes "divisive" causes.

"Continued involvement in UNESCO is not in the national interest of the United States," the State Department spokeswoman said.

The US exit was expected under President Donald Trump, who also ordered withdrawal from the United Nations Educational, Scientific and Cultural Organisation in 2017 during his first term. President Joe Biden then reestablished US membership.

State Department spokeswoman Tammy Bruce described UNESCO as working "to advance divisive social and cultural causes" and being overly focused on UN sustainability goals, which she described as a "globalist, ideological agenda".

Bruce also highlighted what she said was the body's anti-Israeli position in admitting Palestine as a state.

"UNESCO's decision to admit the 'State of Palestine' as a member state is highly problematic, contrary to US policy, and contributed to the proliferation of anti-Israel rhetoric within the organisation," Bruce said.

The UN organisation describes its mission as promoting education, scientific cooperation and cultural understanding.

It oversees a list of heritage sites aimed at preserving unique environmental and architectural gems, ranging from the Great Barrier Reef off Australia and the Serengeti in Tanzania to the Athens Acropolis and Pyramids of Egypt.

Trump was not the first to pull the United States out of UNESCO.

President Ronald Reagan ended US membership in the 1980s, saying the agency was corrupt and pro-Soviet. The United States reentered under the presidency of George W. Bush.

The move is a blow to the Paris-based agency, founded after World War Two to promote peace through international cooperation in education, science, and culture. The New York Post also reported on the US withdrawal, citing a White House official.

Trump took similar steps during his first term, quitting the World Health Organisation, the UN Human Rights Council, a global climate change accord and the Iran nuclear deal.

He has already decided to withdraw the US from the WHO and halt funding to the Palestinian relief agency UNRWA as part of a review of the US' participation in UN agencies, due to be concluded in August.

UNESCO's full name is the United Nations Educational, Scientific and Cultural Organisation.

The United States provides about eight per cent of UNESCO's total budget, down from about 20 per cent at the time Trump first pulled the United States out of the agency.