The United States will leave the World Health Organization (WHO) next July, the United Nations says.

Key points:

• The US has been a member of the WHO for more than 70 years
• The withdrawal of the WHO's largest contributor has been denounced as misguided
• The US could return as a member of the WHO and Joe Biden has promised to reverse Donald Trump's decision

The WHO revealed the timeline after receiving formal notification of the decision by US President Donald Trump more than a month ago.

Mr Trump had to give a year's notice of the US withdrawal from the Geneva-based UN agency under a 1948 joint resolution of the US Congress, which also obliges Washington to pay financial support.

The United States will depart the WHO on July 6, 2021, and under the terms of the withdrawal, it must meet its financial obligations to the WHO before its exit can be finalised.

The US, which is the agency's largest donor and provides it with more than $US450 million ($648 million) per year, currently owes the WHO about $288 million in current and past dues.

"The Secretary-General … is in the process of verifying with the World Health Organization whether all the conditions for such withdrawal are met," a UN spokesman said.