Valencia have condemned supporters who made apparent racist chants and Nazi salutes to Arsenal supporters following Thursday's Europa League semi-final first leg at the Emirates Stadium.
Arsenal won the tie 3-1, having come from behind. Following the match, footage emerged on social media of supporters in the away end making monkey gestures and Nazi salutes aimed at Arsenal fans.
Both clubs have swiftly moved to condemn the individuals, while anti-discrimination campaigners Kick It Out also called for the perpetrators to be identified and face "the strongest possible punishment" following the "shocking and inexcusable" gestures.
Spanish club Valencia said it "publicly condemns" the individuals involved, expressing "utter disgust and absolute intolerance" to the gestures which in "no way represent" the fanbase.
Valencia will work with its legal team and the appropriate authorities to identify those responsible, who if found to be season-ticket holders will face "corresponding disciplinary action".
The club statement added: "While these actions are completely unjustifiable under any circumstances, VCF is also working to obtain more information about any possible provocations leading up to the verbal and gesticular exchange between the home and away stands."
Arsenal, meanwhile, will help with the investigation and urged anyone with relevant information to come forward.
"We are working with Valencia on this. We utterly condemn such behaviour," a club spokesman said in a statement obtained by Press Association Sport.
"We continue to encourage fans to report incidents and to provide witness statements so effective action can be taken."
Press Association Sport understands six Valencia fans were ejected during the game for foul and abusive language, but it is unclear if those relate to incidents captured by @ollie_campman on Twitter.
On Thursday evening, Alexandre Lacazette had scored a first-half brace to cancel out Mouctar Diakhaby's deserved early opener for the visitors.
Pierre-Emerick Aubameyang added what could prove to be a crucial third goal in the final minute for Unai Emery's side, who ended a run of three straight Premier League defeats.