US President Donald Trump on Monday attacked Britain's public healthcare system in comments that are likely to put his much-delayed visit to the country further into doubt.
"The Democrats are pushing for Universal HealthCare while thousands of people are marching in the UK because their U system is going broke and not working," he wrote in an early morning tweet.
"Dems want to greatly raise taxes for really bad and non-personal medical care. No thanks!"
The tweet came after thousands of people marched through central London on Saturday in support of the National Health Service, which is straining under the weight of winter demand.
NHS staffing levels have been in crisis for months, an issue made worse by a winter flu outbreak.
Despite its current woes, the National Health Service (NHS), which was created after World War II, is a revered institution and Trump's comments are likely to stoke resentment.
The "special relationship" between Britain and the United States has shown some signs of strain since Trump came to office a year ago.
British Prime Minister Theresa May was the first foreign leader to visit Trump following his inauguration in January last year, when she invited him to make a state visit to Britain, hosted by Queen Elizabeth II.
The trip has been delayed, however, and Trump recently pulled out of a plan to open the new US embassy in London, a move British officials blamed on threats of mass protests.
Trump has also angered the British with previous controversial tweets, including retweeting an extremist group's anti-Muslim propaganda and sparring with London mayor Sadiq Khan following a terror attack.
It is not certain why Trump chose to attack the NHS two days after the London protests. 
Trump's own attempts to reverse his predecessor's healthcare reform, known as Obamacare, twice ended in failure, before his party succeeded in eliminating a key element -- the so-called "individual mandate," as part of tax reform.
The measure required individuals to buy coverage as a way to lower costs by ensuring that healthy people were part of insurance pools.
One possible explanation for Trump's criticism was an appearance by Brexit champion Nigel Farage, a personal friend of the president, on Fox News earlier on Monday in which he questioned the feasibility of universal healthcare and blamed the NHS's predicament on immigrants.

Britain defends healthcare system after Trump attack

US President Donald Trump drew a fierce reaction from angry Britons, including health minister Jeremy Hunt, on Monday after criticising Britain's publicly funded healthcare system as "going broke and not working".
Britain's health system delivers free care for all. It is typically one of the most important issues for voters during elections and often regarded as a weakness for May's Conservative, or Tory, Party, whose opponents accuse the government of inadequately investing in it.
Twitter users flooded to defend the NHS, with many pointing out that the march Trump referred to was organised by groups which want to increase the health service's funding, not dismantle it.
The rally drew 60,000 people to central London on Saturday according to one of its organisers, Health Campaigns Together. Protesters demanding more funding for the service marched on Prime Minister Theresa May's office.
Even Health Secretary Hunt, one of the main targets of the protesters' anger, snapped back sharply at Trump.
"I may disagree with claims made on that march but not ONE of them wants to live in a system where 28 (million) people have no cover. NHS may have challenges but I’m proud to be from the country that invented universal coverage - where all get care no matter the size of their bank balance," said Hunt.
Opposition Labour Party leader Jeremy Corbyn tweeted back to Trump: "Wrong. People were marching because we love our NHS and hate what the Tories are doing to it. Healthcare is a human right."