British and French police are trying to identify the Chelsea fans who were filmed preventing a black man boarding a train in Paris before chanting "we're racist and that's the way we like it."
Amateur footage posted online shows the commuter trying to board a metro train in the French capital but a group of fans are shown shouting at and gesturing to him before pushing him out of the carriage when he steps in.
On a second attempt he points to a space where he could stand but is pushed away again as he steps forward, before the group of males erupt into a chant while other commuters look on.
The supporters are thought to have been travelling to the Parc des Princes ground for the Champions League match against Paris St Germain last night which ended in a draw.
Chelsea have issued an appeal for witnesses to help identify those involved and asked anyone with any information to contact them in the strictest confidence at email@example.com
French police have confirmed they have launched an investigation into the incident, and have asked their British counterparts for help.
A statement from the Metropolitan police said: "We are aware of footage currently on the internet allegedly involving Chelsea fans in Paris.
"The Metroplitan Police takes these offences very seriously, no matter where they occur. We will examine the footage with a view to seeing if we can apply for football banning orders, preventing people from travelling to future matches.
"We will of course assist French authorities to identify those people involved and support them in any action they choose to take. At the same tame we will be working closely with Chelsea Football Club."
The incident, footage of which was uploaded to the Guardian website, has been widely condemned.
FIFA president Sepp Blatter tweeted: "I condemn the actions of a small group of Chelsea fans. There is no place for racism in football."
UEFA have no jurisdiction over the matter as it happened away from the ground. But in a statement European football’s governing body said: “UEFA condemns all forms of discrimination and we are appalled by the incident which took place in the Paris Metro on Tuesday.
“However, as it occurred away from the stadium, it is outside UEFA’s remit to act. It is a matter for the local authorities to investigate further and UEFA supports any action that is taken."
UEFA's sentiments were echoed by Piara Powar, head of European anti-racism body the Fare Network, who thinks it would be unfair to blame Chelsea for the behaviour of a small number of the club's fans.
"UEFA’s jurisdiction only extends to inside a stadium. Outside of that it is down to the police, civil authorities and the people that run the metro." Powar told Sky Sports News HQ.
"And I’m not sure actually that we’d get very far sanctioning clubs for the behaviour of their fans in towns and cities. "What we need to see is clear progress on the education work we are doing, clear progress on the messages that they are sending out.
"In that sense it is difficult to fault Chelsea and other clubs. Unfortunately, this is a social phenomenon as much as it is a football phenomenon although the two are inextricably linked."
French police have told Sky Sports News HQ that no arrests were made on Tuesday night at the game or around the ground, and that no violence between fans took place.
But Paris' police chief, on viewing the video, confirmed that racist words and violence were used.
Chelsea released a statement condemning the incident and said it will take action if members are found to be involved.
"Such behaviour is abhorrent and has no place in football or society," the club said.
"We will support any criminal action against those involved, and should evidence point to involvement of Chelsea season-ticket holders or members the club will take the strongest possible action against them, including banning orders."
Professional Footballers Association deputy chief executive Bobby Barnes said: “The PFA condemns the actions of so-called Chelsea supporters in Paris last night as seen in a clip posted today.
“I am extremely saddened that such a great football club has had its name dragged into the gutter by a very ignorant minority who seemingly equate supporting Chelsea and cheering for the likes of Didier Drogba, Ramires and John Obi Mikel, with abusing a fellow passenger on a train who was going about his own business.
“I am sure that Chelsea will seek to take strong action against the supporters shown in the video as the club works very hard through their community and education programmes.”
“I have been in contact with Chelsea and they have expressed equal concern and disgust at the footage.”
Kick It Out chairman Lord Ouseley condemned the incident and called for Chelsea, and football, to avoid complacency over incidents of a similar nature.
Lord Ouseley said: "We know that prejudice is on the increase and that in itself leads to hateful attitudes and this sort of conduct.
"I was shocked that Chelsea fans were still behaving like this. I thought the club had made it quite clear and taken action about stopping any repetition, knowing Chelsea, how hard they've worked on these matters, with fans as well as players that it was unlikely to occur.
"The fact it involved an assault as well, of the individual that they pushed off the train, was even more shocking.
"Clearly it sends out a strong signal to, not only Chelsea, but the whole of football, that you cannot be complacent and think the actions you're taking are sufficient to deal with the scourge of racism, sexism, homophobia and anti-Semitism. We've got to do a lot more and not be complacent."
Kick It Out hopes anyone implicated is banned from football, not just from Chelsea matches.
"We'll support any prosecution," Lord Ouseley added. "Anyone who can be identified, if they have an association with the club, the club said it will take the strongest action, which would include banning those people from going to Chelsea football matches.
"I would hope it would extend to banning them from going to any football match.
"Chelsea need to make it quite clear, once again, that people who carry their prejudices around, please don't come to football.
"We need to see that reinforced by all clubs, because it's happening right across the country, not just one team.
"These attitudes are attitudes that are in our society and football can play a major part in helping to draw attention to ways in which we need to help people to change their attitudes."
Meanwhile, Troy Townsend, from Kick It Out, said the incident shows English football has “a long way to go”.
Speaking on Sky Sports News HQ, he said: “There’s definitely an undercurrent still in our game and fanbase.
“The fact that we’re now starting to do it on foreign shores again is also worrying.
“We tend to think we’re doing so much better in the game over here and it’s Europe who need to get in line with the English game.
“Last night proved we’ve got a long way to go.”