US President Donald Trump has said he is going to halt funding to the World Health Organisation (WHO) because it has "failed in its basic duty" in its response to the coronavirus outbreak.

He accused the UN agency of mismanaging and covering up the spread of the virus after it emerged in China, and said it must be held accountable.

In response, the UN chief said it was "not the time" to cut funds to the WHO.

Mr Trump has been under fire for his own handling of the pandemic.

He has sought to deflect persistent criticism that he acted too slowly to stop the virus's spread by pointing to his decision in late January to place restrictions on travel from China.

He has accused the WHO of having "criticised" that decision and of being biased towards China more generally.

"I am directing my administration to halt funding while a review is conducted to assess the World Health Organisation's role in severely mismanaging and covering up the spread of the coronavirus," Mr Trump told a news conference at the White House on Tuesday.

The WHO is yet to directly respond but UN Secretary General António Guterres said the international community should be uniting "in solidarity to stop this virus".

"It is my belief that the World Health Organisation must be supported, as it is absolutely critical to the world's efforts to win the war against Covid-19," he said.

What is the WHO and who funds it?

The WHO was founded in 1948 and has its headquarters in Geneva, Switzerland. It is the UN agency responsible for global public health, with 194 member states, and aims to "promote health, keep the world safe and serve the vulnerable".

Its funding is made up of membership fees - which are known as "assessed contributions" and calculated based on wealth and population - and voluntary contributions.

The US is the WHO's biggest single funder, providing $400m (£316m) in 2018-19 - just under 15% of its total budget.

China's contribution in 2018-19 was almost $76m in assessed contributions and about $10m in voluntary funding, according to the WHO website.

The second-largest funder is the Bill and Melinda Gates Foundation, which provides 9.76% of the WHO's funds. The UK gives the most of any country apart from the US.

Halting funding for the World Health Organization during a world health crisis is as dangerous as it sounds. Their work is slowing the spread of COVID-19 and if that work is stopped no other organization can replace them. The world needs @WHO now more than ever.

— Bill Gates (@BillGates) April 15, 2020

The organisation launched an appeal in March for $675m to help fight the coronavirus pandemic and is reported to be planning a fresh appeal for at least $1bn.

Bill Gates, the Microsoft founder and philanthropist, said on Twitter: "Halting funding for the World Health Organization during a world health crisis is as dangerous as it sounds."

What is Donald Trump's argument?

"With the outbreak of the Covid-19 pandemic, we have deep concerns whether America's generosity has been put to the best use possible," the US president said.

The US has by far the highest number of coronavirus cases and deaths worldwide- with more than 600,000 cases and 26,000 deaths.

Mr Trump accused the WHO of having failed to adequately assess the outbreak when it first emerged in the city of Wuhan.

"Had the WHO done its job to get medical experts into China to objectively assess the situation on the ground and to call out China's lack of transparency, the outbreak could have been contained at its source with very little death," he told reporters.

"This would have saved thousands of lives and avoided worldwide economic damage. Instead, the WHO willingly took China's assurances to face value... and defended the actions of the Chinese government."

White House reporters pointed out, however, that Mr Trump himself praised China's response to the outbreak and downplayed the danger of the virus at home.

China has been working very hard to contain the Coronavirus. The United States greatly appreciates their efforts and transparency. It will all work out well. In particular, on behalf of the American People, I want to thank President Xi!

— Donald J. Trump (@realDonaldTrump) January 24, 2020

After Mr Trump put travel restrictions on China at the end of January, the WHO did not criticise the US directly. Instead it continued to say it did not recommend restrictions on travel and trade.

What about the lockdowns?

Speaking in the Rose Garden at the White House, President Trump also said that plans to reopen the country were "close to being finalised".

Mr Trump caused a furore on Monday when he said that he, and not state governors, had the authority to lift lockdowns and restart the economy.

But on Tuesday, he changed his position, saying: "The governors are responsible. They have to take charge."

"The federal government will be watching them closely. We will hold governors accountable, but will be working with them to make sure it goes really well."

Experts agree it is the governors who are responsible for policing their states under US law.

Earlier on Tuesday, New York Governor Andrew Cuomo accused President Trump of "spoiling for a fight".

"We don't have a king, we have a president," he said.

New York state is the worst-affected state, with almost 190,000 cases and over 10,000 deaths. However, there are signs of improvement with the number of people there needing hospital treatment falling for the first time.

Why has the WHO faced criticism?

It is not the first time the WHO's response to the outbreak has come under scrutiny.

In February, it said that widespread travel restrictions were not needed to stop the spread of Covid-19 - advice that was eventually ignored by most countries.

In March, the UN agency was also accused of being unduly influenced by China after a senior official refused to discuss Taiwan's response to the outbreak.

Meanwhile, some health experts also say that the WHO's guidance on face masks has led to public confusion.