French prosecutors and British police on Wednesday pledged to investigate footage of self-proclaimed "racist" Chelsea supporters preventing a black man from boarding a Paris subway train.
Amateur footage obtained by The Guardian newspaper captured the incident in a Metro station shortly before Chelsea's 1-1 Champions League draw with Paris Saint-Germain in the French capital on Tuesday evening.
It shows a group of men chanting "Chelsea, Chelsea!" standing in a packed train waiting at a platform.
The unidentified black man repeatedly tries to squeeze into the carriage and they aggressively push him back. The film then cuts to the men chanting: "We're racist, we're racist, and that's the way we like it!"
In a statement, Chelsea said the incident was "abhorrent" and had "no place in football or society".
They added: "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."
French state prosecutors announced that they have opened an investigation into "deliberate racial violence on public transport".
London police said they would assist their French counterparts with their inquiries.
"We will examine the footage with a view to seeing if we can apply for football banning orders, preventing people from travelling from future matches," New Scotland Yard said in a statement.
European football's governing body UEFA said it was "appalled" by the fans' behaviour, but said that because the incident had occurred outside the stadium, it was "outside UEFA's remit" to act upon it.
Sepp Blatter, president of world governing body FIFA, wrote on Twitter: "I also condemn the actions of a small group of Chelsea fans in Paris. There is no place for racism in football!"
England's Football Association said: "The FA, like the club, completely condemn such disgraceful behaviour, which is a criminal offence, and those responsible should face the strongest possible punishment."
- 'Disgusted' -
The footage was filmed by Paul Nolan, a Briton living in Paris. He told The Guardian he was "completely appalled" by what he saw at Richelieu-Drouot station in central Paris.
A Chelsea supporter who claimed to have been on the train said the man had only been pushed away because the carriage was full.
"He tried to get on and a few people were pushing him off because there wasn't much space on the carriage. You couldn't move," Mitchell McCoy, 17, told Britain's Press Association.
"People were saying it was because he was black. It's not true at all."
But Chelsea fanzine editor David Johnstone expressed fears for the club's reputation in light of the incident, telling BBC radio "all the supporters are going to be labelled as racist".
English football grappled with serious racism throughout the 1970s and 1980s, when black players were regularly subjected to verbal abuse by supporters.
It has since been largely disappeared from English grounds, although there have been a number of high-profile incidents involving players in recent years.
Chelsea's captain, John Terry, was banned for four matches and fined £220,000 ($340,000, 300,000 euros) in 2012 after the FA found that he had racially abused an opponent. He retired from the England team as a result.
Herman Ouseley, chairman of anti-racism organisation Kick it Out, said the incident in Paris showed that there was still much work to be done to combat discrimination.
"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," he said. "We've got to do a lot more and not be complacent."
The Football Supporters' Federation, which represents fans in England and Wales, said in a statement: "This is a shocking incident and the overwhelming majority of Chelsea fans will be disgusted by it."
The video can be viewed below: