Sadiq Khan has said Donald Trump is "playing into the hands of Daesh" after appearing to back Hillary Clinton's presidential campaign during his tour of North America.
The London mayor addressed a global progress summit in Montreal with Canadian prime minister Justin Trudeau, ahead of trips to Chicago and New York as part of a five-day visit.
Khan, who was involved in a spat with Trump earlier this year over his call for a temporary ban on Muslims entering the US, told the audience that the Republican candidate's message showed a "lack of understanding".
He said: "Donald Trump said that Muslims from around the world - I'm paraphrasing - would not be welcome into the United States of America.
"Not only does that show a lack of understanding and awareness of the great country that is the USA and its history and legacy, it's also inadvertently playing into the hands of Daesh and so-called Isis because it implies it's not possible to be a Western liberal and mainstream Muslim.
"I think it's important that the USA maintains her role as a beacon for tolerance, respect and diversity.
"I think it's important for those of us who are foreigners to stay out of the US elections. I hope the best candidate wins and I hope she does win with a stomping majority."
Later Khan said he would be open to meeting Trump during his trip, along with any other presidential candidate.
He told the Press Association: "It's not for me to get directly involved in the US presidential election. I'm more than happy to meet candidates to discuss some of the joys of London."
During the summit Khan stressed the importance of integrating ethnic minority communities, telling the audience that "the days of laissez-faire" integration were gone.
"The messages of hate being transmitted into people's bedrooms means that people like Justin, the prime minister of Canada, and people like me, the mayor, have a responsibility," he said.
Khan also said he believed the UK should follow Canada's lead and do more to help Syrian refugees.
Canada resettled 25,000 Syrian refugees between November 2015 and February 2016, compared to the UK which has pledged to resettle 20,000 by 2020.
The mayor told Trudeau: "You are a beacon of how a civilised G7 country should treat those who are vulnerable and need help."
Khan is embarking on a five day tour of North America to show the capital is "open for business" in the wake of Britain's decision to leave the European Union.
He is also stressing the importance of "building bridges rather than walls" - a reference to Trump's proposal to build a wall along the US-Mexico border.
During his visit to New York, the mayor will be introduced to Major League Baseball commissioner, Rob Manfred, to discuss plans to bring games to London and throw the first pitch at a New York Mets game.
He will also visit the Clinton Global Initiative during its annual meeting, where he is expected be joined on stage by Chelsea Clinton