Jeremy Corbyn launched an attack on far-right politics as he addressed an anti-Donald Trump rally on the second day of the US President’s state visit.
The Labour leader spoke to crowds from a stage in Whitehall as thousands of protesters took to London’s streets on Tuesday.
Mr Trump said he refused a request for a meeting with the Labour leader and dismissed reports of demonstrations as “fake news”.
Mr Corbyn, who boycotted a state banquet with the President on Monday evening, said: “In welcoming visitors from the United States, I hope there can be a conversation.
“I am not, absolutely not, refusing to meet anybody. I want to be able to have that dialogue to bring about the better and more peaceful world that we all want to live in.
“But I’m very disappointed, particularly today, on the wonderful festival of Eid, that our Mayor of London Sadiq Khan has been attacked as he has.
“I am proud that our city has a Muslim mayor, that we can chase down Islamophobia, anti-Semitism, any form of racism within our society because racism divides.”
Mr Trump attacked the mayor on Twitter moments before he landed in the UK, reigniting a war of words between the pair.
Mr Corbyn, who did not address the President by name during his speech, said the demonstration showed how determined people are to “achieve a better place and a better world”.
He added: “So I say to our visitors that have arrived this week, think on please about a world that is one of peace and disarmament, is one of recognising the values of all people, is a world that defeats racism, defeats misogyny, defeats the religious hatreds that are being fuelled by the far-right in politics in Britain, in Europe and the United States.
“They have no answers. No answers to young people growing up worried about their future, no answers to communities that have lost their industries, no answers for the people that are desperate in all parts of the world to get somewhere to live, no answers to those people that are desperate to get the medical help and support that they need, no answers to those going through a mental health crisis of any sort all over the world.”
During a press conference with Theresa May on Tuesday, Mr Trump hit back at Mr Corbyn and moved to dismiss reports of widespread protests.
The President said he refused to meet the Labour leader, describing him as a “somewhat negative force”, adding: “I didn’t see the protesters until just a little while ago and it was a very, very small group of people put in for political reasons so it was fake news.”
The Trump Babysitters group estimated tens of thousands of protesters were involved in the demonstrations – fewer than an estimated 250,000 who gathered when Mr Trump visited the UK on July 13 last year.
There were no significant protests outside of London.
Earlier on Tuesday, the 20ft Trump baby blimp, which became the focus of last year’s protest during Mr Trump’s first visit to the UK as President, took to the skies for a second time after permission was granted by the Greater London Authority.
A team of organisers wearing red jumpsuits and hats marked “Trump Babysitters” launched the inflatable of the nappy-clad president clutching a mobile phone to cheers from dozens of onlookers at Parliament Square.
Other protesters gathered in Trafalgar Square before marching to Whitehall.
One was selling toilet paper with Mr Trump’s face printed on it, while a 16ft talking robot of the President sitting on a gold toilet, which says the phrases “no collusion”, “you are fake news” and “I’m a very stable genius” – the audio of which is Mr Trump’s own voice – became a focal point for onlookers.
Supporters of Mr Trump also took to the streets to back him.
Lewis Metcalfe, 28, from Richmond in North Yorkshire, said he took a day off work to travel to London and offer “a difference of opinion”.
“I’m obviously going to be a minority today, said Mr Metcalfe, who was at Parliament Square wearing a Make America Great Again cap.
“I’m not here to troll, to cause a riot or cause disruption.
“I don’t agree with all his policies. He’s not the greatest President in the world but he does get things done.”
There were a number of clashes between pro and anti-Trump groups throughout the day.
One Trump supporter was surrounded by an angry group of protesters shouting “Nazi” in Parliament Square.
Video footage posted on social media showed a milkshake was thrown at him before a scuffle broke out.
The man, who said he was from London but did not want to be named, said he was “angry” to have been targeted.
“I had to fight them off,” he said. “I don’t get intimidated by them fascists.”
Explaining his support for the president, he said: “Because he’s done more than he said he was going to do for America.”
He added: “He’s true to his word when he said he wants to make America great again.”
The man said it is important for the US to be in a good position globally, adding: “If there’s a hiccup in America then it’s a tidal wave in England.”
Another clip showed Trump supporters behind a line of police at the entrance to a pub in Whitehall as a much larger crowd chanted: “Nazi scum off our streets.”
A huge police and security operation is under way, with more than 3,182 officers deployed on Tuesday and road closures in place, while protesters were barred from demonstrating directly outside Downing Street.
Scotland Yard’s Deputy Commissioner Sir Steve House told the London Assembly Police and Crime Committee on Tuesday the policing plan has so far worked “effectively”.
He said the force is not in a position to estimate how much the operation will cost but added the US President’s last visit to the capital cost the Met about £2.9 million.