Reading have apologised to Cardiff supporters after a row erupted over allegations of discriminatory abuse during Saturday's FA Cup fourth round clash between the clubs.
Four travelling supporters have been released under investigation after being arrested by Thames Valley Police on suspicion of racist chanting under the Football Spectators Act.
However, Cardiff demanded an apology after an announcement was made over the public address system at the Madejski Stadium asking "away fans" to refrain from chants which were "not acceptable", and the Royals responded on Tuesday.
A statement on the club's official website said: "As indicated on the day of the game, these incidents were isolated, restricted to a small number of individuals and affected only a minority of supporters attending the match.
"There was certainly no intention to tarnish the reputation of the travelling support on the day, Cardiff City Football Club nor its fanbase in general, who in the overwhelming majority behaved impeccably at the weekend.
"We would like to apologise to all supporters of Cardiff City Football Club who played no part in any discriminatory abuse and feel that their character has been blemished unwarrantedly by the announcement which was made over the PA system at Madejski Stadium.
"Reading Football Club are liaising with the relevant football authorities to consider how football-wide protocol issued to us was implemented in this instance and we will review our procedure regarding public matchday announcements of this nature accordingly.
"However, at both Reading Football Club and Cardiff City Football Club, we remain committed to ensuring that the matchday environment provides a positive experience for all.
"Discrimination of any form is not OK and all supporters who visit Madejski Stadium are reminded that instances of discriminatory behaviour will not be tolerated.
"No further comment can be made by Reading Football Club or Thames Valley Police at this stage so not to compromise the ongoing investigation."
The arrests were made after two incidents, described by Reading as "isolated", during the 1-1 draw.
In the aftermath, Cardiff chief executive Ken Choo said in a statement: "The announcement made at Reading this weekend was both damaging and hurtful and we would welcome a public apology from them to our supporters.
"I look forward to the conclusion of the police investigation, at which point I am confident that the reputation of our club and fans will be fully and unequivocally restored."
The sides are due to meet again in the Sky Bet Championship at the Cardiff City Stadium on Friday evening ahead of next Tuesday's replay in South Wales.
