London - Video footage of self-proclaimed racist Chelsea fans pushing a black man off a Paris metro train was "extremely disturbing and very worrying", British prime minister David Cameron said on Wednesday.
"It's obviously potentially a criminal offence and so I'm sure the French police will be looking at it very seriously," 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."
The Guardian newspaper obtained amateur video footage filmed shortly before Chelsea's Champions League game at Paris Saint-Germain on Tuesday that showed a group of the club's fans preventing a black man from boarding the crowded train.
The men onboard twice push the man back on to the platform and are then heard chanting: "We're racist, we're racist, and that's the way we like it!"
French and British police have launched investigations into the incident, while Chelsea branded it "abhorrent" and vowed to ban any supporters found to have been involved from attending their matches.
The incident also drew condemnation from the Football Association, European governing body UEFA, world governing body FIFA, French politicians and various anti-discrimination groups.