The World Health Organization (WHO) has urged US President-elect Donald Trump to expand Obamacare, the signature policy of the outgoing President that Mr Trump has called an "incredible economic burden".

The WHO said it wanted Mr Trump's administration to "make sure that the social contract is expanded and that all U.S. citizens have access to health care".

The real-estate magnate has appointed Congressman Tom Price, a fierce critic of the Affordable Care Act, as his health secretary. During his campaign Mr Trump promised that on day one of his presidency he would ask Congress to "immediately deliver a full repeal" of the Act.

Agnes Soucat, the WHO's director of health system governance and financing, said there were various ways of providing health cover to more people, and it amounted to "political choices."

The United States is the only country among the 35 member states of the Organisation for Economic Cooperation and Development not to provide universal health care, a key UN sustainable development goal for 2030, she said.

Obamacare has provided some 25 million previously uninsured Americans with health cover. Republicans say it has created unwarranted government intervention in personal healthcare and private industry.

Mr Price has long championed a plan of tax credits, expanded health savings accounts, and lawsuit reforms to replace Obamacare.

He has insisted that Republicans can keep the protections for those with existing medical conditions without mandating that all individuals carry coverage or pay a penalty to support an expanded insurance pool.

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Republicans are divided over how quickly an Obamacare repeal should go into effect, with some saying a delay would give them time to work on a replacement, instead of throwing millions of Americans out of their health insurance with no substitute.

Ms Soucat said: "There are different strategies to make universal health care particularly pro-poor. So what we are saying is, yes, this would be a setback if people would lose coverage."