Bulgaria coach Krasimir Balakov has apologised to the England team for the racist taunts they were subjected to during Monday's European Qualifier.
Raheem Sterling, Marcus Rashford and Tyrone Mings were abused during England's 6-0 victory - and four arrests have now been made by Bulgarian police.
Bulgaria coach Balakov issued a statement on Facebook on Tuesday, in which he said: "I condemn unconditionally all forms of racism as unacceptable behaviour that contradicts normal human relationships.
"I think that this form of prejudice should be buried deep in our past, and nobody should ever be subjected.
"I trained many Bulgarian teams with players of different backgrounds and never judged anyone about the colour of their skin. In addition, I have always actively participated in all initiatives involving unprivileged people or the needy.
"My comments before the game against England that Bulgaria had no problems with racism are based on the fact that the local championship has not seen such a problem on a large scale.
"There may have been isolated cases, but it's definitely not something you see in the stadium.
"The majority of football fans do not take part in such chants, and I believe that was also the case in the game against England.
"One thing I would like to say very clearly is that as the stadium in Sofia has reported cases of racial discrimination, I sincerely apologise to the English footballers and those who feel offended."
'I feel embarassed' - Bulgaria skipper
Bulgaria captain Ivelin Popov says he is "embarrassed" by his fans' actions.
Popov bravely confronted his own supporters at half-time in an attempt to get them to stop their racist abuse and was subsequently praised for his courage by Rashford on social media after the game.
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Speaking after the match, Popov said: "Of course I feel embarrassed.
"We are 11 v 11, it doesn't matter your colour, it's no problem, we are all the same, we are one very big family in football, everybody and only we, if we are together, can we stop these bad things.
"It was important that I spoke like this because it's a very big problem for everybody, for our federation, for England and if they said more bad words, even one more time, then maybe they would finish the game.
"We would have such a big punishment and this is no good for Bulgarian football because if some other players want to come here, they hear what is said and how they speak bad, then this is no good for everybody. But when you start to speak to them, afterwards they understand. I think in the second half was better."
The midfielder, who has 88 international caps, does not understand why some Bulgaria fans racially abused England's players as teams they support also contain black players.
Popov continued: "I don't want it to be like this, it's not good for us, the federation and our country. How do I feel? I don't feel good because we didn't play well, we lost 6-0 and also this what happened was terrible.
"It must stop. In this country, we have a team like Ludogorets, who have players from every country, I never [heard] this sort of problem in the Bulgarian championship and I don't know why they made like this because many fans are fans and supporters of English football.
"There are fan clubs from Chelsea, Liverpool, Manchester, it's incredible and I don't know why they made this. For me, it's incredible, a surprise."
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