Croatia defender Domagoj Vida apologised after his team's World Cup semifinal victory over England on Wednesday after speaking out in support of Russia's neighbour and adversary Ukraine.
Spectators at Wednesday's match in Moscow booed and whistled the Croatia centre-back, after a video posted online earlier in the week showed Vida, a former player with Ukrainian club side Dynamo Kiev, saying "Glory to Ukraine!"
Vida, speaking in Russian in a live postmatch interview with the Rossiya 24 state TV channel late on Wednesday, said: "I know I made a mistake and I would like to apologise again to Russian people.
"I'm sorry. That's life. You have to learn from your mistakes."
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Russia's relations with Ukraine have been fraught since Moscow annexed Crimea in 2014 and backed pro-Russian separatists in eastern Ukraine.
The booing and whistles rang out each time Vida touched the ball in the semifinal against England, starting about 30 minutes into the first half.
It did not appear to be coming from sections of the stadium where England supporters were concentrated. There were significant numbers of Russians in the stadium.
World football's governing body FIFA ruled that Vida's comments in the video were not in keeping with tournament rules about political neutrality and its disciplinary committee issued a formal warning to the defender, which lead to FIFA's Facebook page being inundated with angry messages from Ukrainians.
FIFA hit Ognjen Vukojevic, a member of Croatia's coaching staff who appeared in the video with Vida, with a fine 15,000 Swiss francs. Vukojevic was subsequently fired from his role with the national team.
In an earlier statement released by the Croatian Football Federation, Vida, 29, said his comments were not intended to be political and were related to his former career with Dynamo Kiev.
"Our intention was not to offend anyone..." Vida said. "I sincerely hope that this message will not be understood as anything else but an expression of gratitude to our friends in Ukraine for their support."