Donald Trump has insisted the US wants "nothing to do" with the NHS in post-Brexit trade talks as he sought to repudiate opposition claims that the health service would be "up for sale".
On a visit to the UK, the US President claimed he had no interest in increased market access to the NHS for US firms even if handed on a "silver platter".
But Labour leader Jeremy Corbyn said he still had "very serious concerns".
And the SNP said MPs should pass a law to exclude the NHS from discussions.
Boris Johnson said the Conservative election manifesto had "categorically ruled out" any NHS services, or drug prices, being up for negotiation.
In June, the US president suggested the health service would form part of negotiations over a possible future trade deal after the UK leaves the EU, saying: "When you're dealing in trade, everything is on the table."
But speaking on Tuesday morning as he and other world leaders prepared for a summit to mark the 70th anniversary of Nato, he issued a different message.
"I don't even know where that rumour started," he told journalists. "We have absolutely nothing to do with it. If you handed it [the NHS] to us on a silver platter, we want nothing to do with it."
Mr Trump's visit comes at hugely sensitive time, with less than 10 days to go before the election - and with the issues of Brexit and the NHS having largely dominated the campaign so far.
The US President insisted he would be "staying out" of the election. While he remained a "fan of Brexit" and thought Mr Johnson was "very capable", he said he would be prepared to "work with anybody" in No 10.
In October, he suggested Mr Corbyn would be "bad" for the UK and declined an offer to meet the Labour leader during his state visit.
Mr Corbyn has repeatedly claimed that the NHS would be "up for sale" if the Conservatives hold onto power. At a campaign event last week, the Labour leader showed an unredacted report that gave details of meetings between US and UK officials.
The document shows the US is interested in discussing drug pricing - mainly extending patents that stop cheaper generic medicines being used - and refers to the US policy of making "total market access" a starting point in any trade talks.
The Labour leader welcomed Mr Trump's latest comments but said he was far from reassured by them.
"I'm pleased that he's said that but, if that's the case why have these talks gone on for two years?" he told BBC Radio 2's Jeremy Vine show.
"Why have they been kept secret? I think there is very very legitimate grounds for very very serious concern here."
'Load of salt'
Mr Corbyn said if he was introduced to Mr Trump at a reception at Buckingham Palace later, which both are attending, he would impress on him how "precious" the NHS was to the British people and make clear a Labour government would discontinue trade talks if it was not excluded.
On a trip to Salisbury, the prime minister described the opposition's claims as "pure Loch Ness Monster, Bermuda triangle stuff".
"I can categorically rule out any part of the NHS will be on the table in any trade negotiation... including pharmaceuticals."
And Foreign Secretary Dominic Raab suggested Labour was only raising the issue because it had "no plan for Brexit and no plan for the economy".
Speaking to BBC Radio 4's Today programme, Mr Raab ruled out any privatisation of the NHS "under the Conservatives' watch or this prime minister's watch". Trade decisions would be made by the next government "in the best interest of patients and consumers", he added.
The Liberal Democrats' foreign affairs spokesman, Chuka Umunna, said Mr Trump's comments should be taken "with a lorry load of salt".
He added: "Trump has repeatedly made clear in the past that everything including the NHS will be on the table in future negotiations."
And SNP leader Nicola Sturgeon said its MPs would be pressing for legislation to ringfence the NHS from any involvement in a future deal.
"I don't want the future of our NHS to be dependent on trusting the word of Boris Johnson or Donald Trump," she said at a campaign rally in Perth.
"Let's have legislation that explicitly and in statute takes any risk of trade negotiations to the NHS away, and make absolutely clear that the NHS not just will not be on the table but could not be on the table in any trade negotiations."
Nigel Farage called on the US president to challenge the "complete fib" that the Tories would "sell the NHS" to him in a trade deal.
"He has been accused by the Labour Party of wanting to buy the National Health Service," the Brexit Party leader told BBC Breakfast. "It isn't true, I know it isn't true, and I think it would be wholly appropriate for him to say that."