The Chelsea chairman, Bruce Buck, has published an open letter to the club’s supporters condemning the actions of a “mindless” minority at recent games and vowing not to rest “until we have eliminated all forms of discrimination from our club”.

The 700-word letter was launched on Chelsea’s website on the day Uefa launched an investigation into allegations that fans sang an antisemitic chant during last week’s Europa League tie in Hungary. The incident in Budapest, where some travelling fans were photographed holding a Chelsea Headhunters flag featuring a Nazi symbol, came four days after Raheem Sterling was subjected to alleged racist abuse in a win over Manchester City, with four supporters subsequently suspended by the club.

“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 wrote. “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.

“We have been carrying out our own investigations into these events while co-operating fully with authorities. We have already suspended four individuals pending investigations and will continue to take the strongest possible action against anybody found to have been using discriminatory words or gestures. But we must all come together to stamp out these ugly scenes.”

The recent flurry of incidents, described by Buck as a “plague”, has dismayed the Chelsea hierarchy, not least given their extensive efforts to combat discrimination. Buck noted that the club had been trying since 2010 to “rid the game of the Y-word, and have frequently reiterated since, that what other clubs may deem acceptable from their supporters in the way of personal identification does not alter our position of zero tolerance”.

He added: “Clearly, there remains a way to go on this journey, but we will not rest until we have eliminated all forms of discrimination from our club. We will continue to work alongside our fans, anti-discrimination organisations and football authorities to create an environment where everyone feels welcome and valued. If you do not share these values, this is not the club for you. We must not allow a small minority of fans to bring further embarrassment upon us.”

If Uefa determines that the chant from a section of the travelling support in Hungary did insult “the human dignity of a person or group of persons on whatever grounds, including skin colour, race, religion or ethnic origin”, then the minimum sanction to which Chelsea would be subjected is the partial closure of Stamford Bridge at a Europa League game. Its report will be submitted in mid-January.