UEFA today 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 yesterday branding the incident "a real disgrace".
Having been satisfied by the Dutch FA's initial assurances the abuse was not racially-motivated, UEFA announced this morning 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."
Former Holland star Ruud Gullit, now a UEFA representative, said today: "Everybody was very, very upset".
UEFA were yesterday satisfied by claims the abusive chanting from the stands was actually a protest against the fact Krakow had not been made one of the host cities for Euro 2012.
The problems occurred when players began Wednesday's training session by doing laps of the pitch only to be greeted at one end of the stadium with alleged monkey noises and loud jeers.
The abuse was said to be bad enough for the squad to move their equipment and training drills as far away as possible from the affected area.
Van Bommel told anyone who denied the incident was racially motivated to "open your ears", adding: "If you did hear it, and don't want to hear it, that is even worse."
Holland arrived in Kharkiv, Ukraine, this afternoon and were scheduled to hold a press conference ahead of their Euro 2012 Group B opener against Denmark tomorrow.
There were always fears over racism at this summer's tournament, with BBC's Panorama programme last week highlighting the problem at Krakow's two major clubs, Wisla and Cracovia, as well as in Ukraine.
UEFA president Michel Platini said on Wednesday referees would halt or even abandon matches if there was serious racism from the stands during Euro 2012.
Mario Balotelli - whose Italy side are also based in Krakow - had threatened to walk off in protest if he was racially abused during games but Platini warned any player who did so would be yellow carded.
The families of two of England's black players, Alex Oxlade-Chamberlain and Theo Walcott, have already decided against travelling to the tournament because of the potential problems.
Powar said on Wednesday he was more concerned about racist abuse at Euro 2012 than at any previous tournament.
He added today: "It's a great shame for this to happen on the eve of the tournament."