London - Chelsea chairman Bruce Buck has blamed a "deeply unpleasant but vocal minority" for shaming the club's fans in an open letter following recent incidents of abuse.
The Premier League club and police opened investigations after alleged racist abuse was directed at Manchester City's Raheem Sterling by a section of home supporters at Stamford Bridge earlier this month.
Chelsea suspended four supporters pending an investigation.
And minutes into last week's Europa League clash with Vidi in Budapest, a vocal minority of Chelsea fans were heard singing a derogatory chant about Tottenham supporters, featuring anti-Semitic language.
European governing body UEFA on Tuesday announced it had launched an investigation into the chants, with the results due to be published next month.
"After recent events, I wanted to take this opportunity to reach out to our community and fans to condemn the actions of a few mindless individuals at some of our recent matches," Buck said in the letter published on Tuesday on the club's website.
"These actions are unacceptable and unwelcome both in our club and in football."
"A deeply unpleasant but vocal minority which refuses to join us in the 21st century has shamed the great majority of our decent, well-behaved fans."
He said the club "must all come together to stamp out these ugly scenes", listing a number of initiatives that Chelsea have been involved in to tackle discrimination.
"If you do not share these values, this is not the club for you," he said.
"We must not allow a small minority of fans to bring further embarrassment upon us, and will continue to take the strongest possible action against them."