Fears over Euro 2012 being overshadowed by racism returned on Friday, after UEFA confirmed that there was racist chanting at the Netherlands' public training session this week in the Polish city of Krakow.

European football's governing body, though, stopped short of launching a formal investigation, saying it had not received a formal complaint from the Dutch football federation (KNVB).

The revelations, which follow comments published on Friday from team captain Mark van Bommel in the Dutch newspaper De Telegraaf, could not have come at a worse time for Euro 2012 organisers, with the tournament due to kick off on Friday evening.

Co-hosts Poland and Ukraine have already been forced to reject claims that racist violence is rife at their football grounds, which has led to governments of some participating nations to warn travelling fans to be on their guard.

Van Bommel, who led the Oranje on a solemn tour of the former German Nazi death camp at Auschwitz near their Krakow base earlier this week, was quoted as saying by the daily: "We all heard the monkey chants. We can't accept that.

"We reacted well (coach Bert van Marwijk took them to the other side of the pitch) and the situation was sorted."

But he warned: "If any of us is targetted by monkey chants during our matches we won't accept it. If we hear anything like that during a game, I'll immediately go to the referee to ask him to intervene."

He also hit out at anyone who chooses to ignore racist chants.

"You need to open your ears. If you hear them but don't want to hear them, that's worse," he said.

A senior UEFA official had told AFP on Thursday that a small group of protesters targeted the Dutch team's training ground in Krakow on Wednesday and were unhappy at Krakow not being one of the four Polish host cities chosen for the tournament.

But they had contacted the Dutch team and were initially told that the protests were not racist in nature.

Van Marwijk, who is van Bommel's father-in-law, even said afterwards that there was an "extraordinary atmosphere" at the training venue.

"UEFA has now been made aware that there were some isolated incidents of racist chanting that occurred at the open training sessions of the Dutch team (on Wednesday) in Krakow," it said in a statement on Friday.

"UEFA has not yet received any formal complaint from the KNVB."

The Netherlands play their opening match in Group B against Denmark on Saturday in the Ukrainian city of Kharkiv.

Last month, BBC television aired a documentary suggesting that far-right gangs used football matches in both host nations as recruiting grounds and showed footage of fans making Nazi salutes and monkey noises at black players.

The British government, among others, issued a travel warning to fans about the risk of racist violence, prompting the families of two black England players to say they would stay at home.

Former England captain Sol Campbell, who is black, publicly advised black and ethnic minority fans not to travel while Italy's Mario Balotelli even said he would walk off the pitch if he were subject to racial taunts.

Poland, Ukraine and UEFA president Michel Platini have said that racism was a social problem across Europe and not confined to the host countries.

Platini told reporters in Warsaw on Wednesday that said measures were in place to ensure that racist incidents are kept to a minimum and would support referees who now had the power to take players off the pitch.