Police are investigating racist chanting at St Pancras Station by men believed to be Chelsea supporters returning from Paris.
The alleged incident comes after a number of Chelsea fans are said to have racially abused a black man on a Paris metro train.
British Transport Police said the men chanted as they walked through the station on Wednesday evening.
“The racist chanting was reported by a member of the public who was disgusted by the behaviour of the men who had travelled on the 18.40 service from Paris Gard du Nord," Superintendent Gill Murray said.
"The men shouted as they walked through the station having alighted from the train a short time earlier.
“If you travelled on the train from Paris or were at the station and have information which can assist our investigation I would urge you to get in touch as a matter of urgency.”
French president Francois Hollande has today spoken to the victim of the Paris Metro incident, according to Le Parisien newspaper.
Mr Hollande praised the 33-year-old, known only as Souleymane, and reportedly thanked him for the dignity he had shown in his public remarks over the incident.
Police have released three images of men they believe were involved in an allegedly racist incident on the Paris Metro.
Five Chelsea fans have been banned from Stamford Bridge over the incident already after a black man was pushed off a Paris train in an apparently racially-motivated incident involving Chelsea supporters on Tuesday.
The Metropolitan Police said in a statement: "The three men are thought to be Chelsea Football Club fans who were travelling to the match against Paris Saint-Germain, at Parc des Princes."
Anyone who believes they may know the men are asked to contact the MPS on 101 or call Crimestoppers anonymously 0800 555 111.
Chelsea have said that two more people have been banned from Stamford Bridge as a result of ongoing investigations into the incident on the Paris Metro.
In a statement Chelsea said: "If it is deemed there is sufficient evidence of their involvement in the incident, the club will issue banning orders for life."
A further two people have been suspended from Stamford Bridge after the incident on the Paris Metro... http://t.co/YP9RWTQeUU
Three people had already been suspended over the incident on Tuesday.
The black man who was pushed off a Paris Metro train by Chelsea fans chanting a racist song said the incident is the club's "responsibility".
The man, identified only as 33-year-old Souleymane, said he not yet received any contact via his lawyer from the Premier League club after he was left "humiliated" on Tuesday evening.
He told BBC Radio 5 Live Drive:
For me, it's a humiliation. I was humiliated in my country. I was humiliated in front of my family, humiliated in front of my mother and father.
Of course it's Chelsea's responsibility. It's their supporters.
They (the fans) didn't say Paris, they said Chelsea. Chelsea should call my lawyer. And they haven't done that yet. It's their supporters. The director general of PSG has called my lawyer but Chelsea haven't contacted my lawyer.
Chelsea have said they are "appalled" and have apologised to the victim, while manager Jose Mourinho said he was "ashamed" of the fans involved. The club have suspended three people from its Stamford Bridge ground and are helping police in the UK and Paris.
Chelsea have issued an apology to the black man who was racially abused by club supporters on the Paris Metro on Tuesday nightRead the full story ›
Jose Mourinho and Chelsea feel "ashamed" about the racist incident involving fans in Paris, but he refuses to be connected with culpritsRead the full story ›
A Chelsea fan embroiled in a racism row on the Paris Métro appears to have been suspended by his employers.
Josh Parsons, 21, was identified on Twitter as being among a large crowd of fans present when a black man was pushed off the train, with supporters going on to chant: "We're racist, we're racist, and that's the way we like it."
In a statement published on the company's Facebook page, The Business & Commercial Finance Club said:
We are utterly opposed to racism in all of its forms and would never tolerate racist conduct among any employee.
We are investigating the events in Paris and Mr Parsons will not return to work until we have conducted a full and thorough investigation.
Chelsea Football Club has identified and suspended three fans after the racist incident on the Paris Metro. In a statement this evening the club said it was working with French authorities as they worked to identify further suspects involved.
Today the victim of the racist chanting spoke out to call for the fans to be found and punished. Sports Editor Steve Scott reports.
The man prevented from boarding a train in Paris by Chelsea supporters chanting racist slogans said they should be caught and punished.
The man told a French newspaper that although he could not understand what the men were saying, he knew he was being targeted because of the colour of his skin.
As police in France work to trace the accused supporters, this evening Chelsea FC said it was suspending three people from Stamford Bridge as investigations continue.
ITV News reporter Rebecca Barry reports: