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Sergio Busquets (left) is accused of racially abusing Marcelo (right)

A racism row erupted prior to the Barcelona-Real Madrid Champions League semi-final second leg on Tuesday.

Real published a video on their website showing Barca's Sergio Busquets allegedly calling full-back Marcelo "mono" (monkey) during the first leg.

Real coach Aitor Karanka spoke of "racist insults" before the game which Barcelona won 3-1 on aggregate.

But Barcelona coach Pep Guardiola countered: "My players are an example of professionalism and honesty."

The dispute further inflamed tensions between the bitter Spanish rivals after a fiery first leg in Madrid, which Barcelona won 2-0.

Barca reserve goalkeeper Jose Pinto, Real midfielder Pepe and coach Jose Mourinho were all sent off, with the Portuguese claiming afterwards that the Catalan side receive preferential treatment from referees.

Both sides submitted complaints to Uefa about the other's behaviour, but they were rejected on Monday. Meanwhile, the European governing body is investigating its own charges against the clubs.

With Mourinho choosing not to speak to the media ahead of the second leg at the Nou Camp, it was left to Karanka to bemoan Uefa's decision not to act on Real's claims of gamesmanship by Barcelona's players.

He said: "The match has been overshadowed by Uefa's resolution - it's on another plane now.

"We have been punished [with the suspensions for Pepe, Sergio Ramos and Mourinho], but there are [Barcelona] players who didn't respect the principles of fair play or who made racist insults, covering their mouths, who will be on the pitch.

"We say over and over there are double standards."

Rejecting the accusations, Guardiola insisted the Catalan club taught their players good values through the youth academy at La Masia.

"Real might think we are unsporting but I think exactly the opposite," he said. "Fourteen of 20 players in the squad have grown up in this house and they all respect the values of the house.

"Mourinho was at Barcelona for five years and he knows our values: to win, fight and earn respect by respecting your rival."

Guardiola added: "Tomorrow it all finishes. We are playing for a place in the final, not to beat Real Madrid."

Barca midfielder Xavi also talked about the negative impact of last Wednesday's game.

"From my point of view everything that has been happening is sad," said the Barca playmaker. "It would be nice to talk about football instead and not these ridiculous issues.

"We will try not to let any of this tension affect us, which is negative for football and sport in general. It's impossible but we will try."

Mourinho was banned from the touchline as his side tried to overhaul a 2-0 first-leg deficit at the home of the Catalan giants.

But despite Marcelo's goal equalising after Pedro's opener for the Catalans, Barcelona progressed to the final at Wembley on 28 May where they face the winner of the tie between Manchester United and Schalke 04.

United play Germany's Schalke on Wednesday at Old Trafford with a 2-0 cushion from the first leg.