British Prime Minister David Cameron has said a video of self-proclaimed racist fans who were filmed preventing a black man from boarding a Paris subway train, was "extremely disturbing and very worrying".
Amateur footage obtained by The Guardian newspaper captured the incident in a Metro station shortly before Chelsea's Champions League match with Paris Saint-Germain in the French capital last night.
It shows a group of men chanting "Chelsea, Chelsea" standing in a packed train waiting at a platform.
The unidentified black man repeatedly tried to squeeze into the carriage and they aggressively pushed him back.
The film then cuts to them chanting: "We're racist, we're racist, and that's the way we like it."
"It's obviously potentially a criminal offence and so I'm sure the French police will be looking at it very seriously," Mr Cameron told London radio station LBC in an interview.
"I know the British police will give every assistance that they can. I'm sure Chelsea will co-operate with that fully. These are very very serious matters."
In a statement, Chelsea said: "Such behaviour is abhorrent and has 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."
FIFA president Sepp Blatter and UEFA have joined Chelsea in condemning the incident.
I also condemn the actions of a small group of Chelsea fans in Paris. There is no place for racism in football!— Joseph S Blatter (@SeppBlatter) February 18, 2015
UEFA's statement read: "We are appalled by the incident which took place in the Paris Metro on Tuesday."
However, European soccer's ruling body, which also has a zero tolerance policy towards racism in stadiums, distanced itself from being able to take action against the fans or the London club.
"As it occurred away from the stadium, it is outside UEFA's remit to act," it said.
"It is a matter for the local authorities to investigate further and UEFA supports any action that is taken."
Former England striker Stan Collymore, who campaigns against racism, tweeted: "Chelsea fans. Save your spite for those on the train, I'm sure you'll want to see them banned from holding season tickets at your club."
The footage was filmed by British man Paul Nolan, who lives in Paris.
He told The Guardian he was "completely appalled" by what he saw at Richelieu-Drouot station in central Paris.