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 yesterday.
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 US.
"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 yesterday, 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."
