UEFA have vowed to crack down on racism at the European Championship after they and the Dutch Football Association acknowledged Holland's black players were abused during a training session in Krakow.
Members of Bert van Marwijk's squad were allegedly subjected to monkey chants at Wisla Krakow's Miejski Stadium on Wednesday, with captain Mark van Bommel branding the incident "a real disgrace".
Having been satisfied by the Dutch FA's initial assurances the abuse was not racially-motivated, UEFA announced they had been made aware of "isolated incidents of racist chanting". European football's governing body confirmed they would consider increasing the number of stewards at open training sessions in order to eject fans if there was a repeat.
They said in a statement: "UEFA has now been made aware that there were some isolated incidents of racist chanting that occurred at the open training session of the Dutch team. Should such behaviour happen at further training sessions, UEFA would evaluate the operational measures to be taken to protect the players.
"UEFA has a zero-tolerance policy when it comes to discriminatory behaviour and has given the power to referees to stop matches in case of any repeated racist behaviour."
Press Association Sport understands UEFA's statement followed lobbying from the FARE (Football Against Racism in Europe) network. The Dutch FA issued their own statement this afternoon confirming some of their players heard "possible monkey chants".
They added: "Although KNVB will not make an official complaint to UEFA, they are more than willing to answer questions of UEFA in this respect."
FARE chief executive Piara Powar, who earlier urged UEFA and the Dutch FA to acknowledge the racist abuse, called on teams to play their 'open' training sessions behind closed doors if necessary. He said: "Public displays of intolerance like this - xenophobia, anti-semitism and racism - can't be allowed to go on.
"If that means playing behind closed doors and closing down that whole open-training system then I think that needs to be done."
Holland winger Ibrahim Afellay, who is black, said in De Telegraaf: "The only thing that you can say is that there are more madmen roaming than trapped. I hear certain things. When you're a footballer, you must be strong, because you hear it all the time - when you enter the pitch, when you take a throw-in, or when you take a corner."