French and British police on Wednesday launched a hunt for self-proclaimed "racist" Chelsea football fans who pushed a black man off a Paris metro train.
A new storm of controversy over racial abuse came to the fore in the sport after amateur video emerged showing the fans chanting: "We're racist, we're racist, and that's the way we like it!"
English Premier League leaders Chelsea called the affair "abhorrent".
International football leaders also condemned the incident in the centre of the French capital ahead of Chelsea's Champions League game against Paris Saint Germain on Tuesday night.
The British supporters repeatedly pushed back the man each time he tried to get on the packed carriage, according to film obtained by The Guardian newspaper.
French prosecutors said they have opened an investigation into "deliberate racial violence on public transport." "We will work with British police, these people must be known," a French police source told AFP London police confirmed that they would assist the French investigation.
"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," said a New Scotland Yard statement.
The images shocked the football establishment.
In a statement, Chelsea called the incident "abhorrent" and said it had "no place in football or society". "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."
European football's governing body UEFA said it was "appalled" by the behaviour, but because the incident had occurred outside a 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."
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."
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. While that problem has eased, there have been a number of high-profile incidents involving players in recent years.
Chelsea captain, John Terry, was banned for four matches and fined £220,000 ($340,000, 300,000 euros) in 2012 for racially abusing an opponent. He retired from the England team as a result.
Herman Ouseley, chairman of anti-racism organisation Kick it Out, said the Paris incident highlighted how work still has to be done against 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."