Thousands of people joined a May Day rally in London on Sunday where Jeremy Corbyn sought to placate concerns that the Labour Party has an anti-Semitism problem.
The Labour leader joined crowds at Clerkenwell Green to mark the international day honouring workers.
Speaking to demonstrators from the top of a red bus, Corbyn said his party was "united" and stood "against racism in any form".
Corbyn said: "We stand in solidarity now against the growth of the far right across Europe that are more interested in blaming migrant workers, blaming victims of war who are refugees than facing up to the reality that we are all human beings living on one planet and you solve problems by human rights, humanity and justice and respect, not by blaming minorities.
"And so we stand absolutely against anti-Semitism in any form.
"We stand absolutely against racism in any form. We stand united as a Labour movement, recognising our faith diversity, our ethnic diversity.
"And from that diversity comes our strength. That is the strength of our movement."
His comments come after a turbulent week for the Labour Party after Ken Livingstone was suspended from the party following comments he made about Hitler and Zionism.
Corbyn is the first Labour leader to attend a May Day rally in 50 years.
Frances O’Grady, general secretary of the TUC, wished the crowd a happy May Day and sent a special message of solidarity to BHS workers.
She said: “We stand by you."
The rally celebrates "what was won by workers' campaigning over many years", including the NHS, education, pensions and affordable housing, which organisers claimed were under attack by the austerity agenda.
With placards brandishing slogans such as “Cameron must go”, the rally marched to Trafalgar Square where more speakers addressed hundreds of workers.
Shadow chancellor John McDonnell was expected to speak at Clerkenwell Green with Corbyn but is attending another May Day rally in Glasgow.
A brass band played as the rally marched through the streets of London, along the Strand, to Trafalgar Square.
Workers held placards representing dozens of unions, including Unite and the RMT.
Many held banners and placards calling for Prime Minister David Cameron to resign.
There was a large contingent calling for international solidarity on human rights and trade union rights. Several others held placards in support of junior doctors.
At one point the rally was stalled as it passed along the Strand where a group from Unite set off red smoke flares.
