Bulgaria coach Krasimir Balakov has apologised after initially saying he did not hear the racist abuse directed at England players during Monday's Euro 2020 qualifier in Sofia.
England claimed a 6-0 win but the match was marred by incidents in the stands, which were reported to officials and resulted in two delays to the action before half-time.
UEFA opted to charge the Bulgarian Football Union (BFU) for "racist behaviour (chants, Nazi salutes)", with local reports indicating four people have been arrested in connection.
BFU president Borislav Mihaylov resigned under pressure from Bulgarian prime minister Boyko Borissov in the wake of the furore.
Before the match, coach Balakov claimed England had a bigger problem with racism in football than his own country, then insisted after the game he had not heart the chanting.
But he has since issued an apology after accepting racist abuse did occur.
In a letter posted to his official Facebook page, Balakov wrote: "I condemn all forms of racism as an unacceptable behaviour that contradicts normal human relations.
"I think that this form of prejudice should be buried deep in our past, and no one should ever be subjected [to it].
"I have trained many Bulgarian teams with players of different origin and never anyone judging by the colour of their skin. In addition, I have always participated actively in all initiatives involving privileged people or those who need to be involved.
"My comments before the game against England that Bulgaria did not have problems with racism is based on the fact that the local championship did not see such a problem on a large scale.
"There may have been individual cases, but it's definitely not something you see at the stadium. The majority of football fans do not participate in this kind [of behaviour], and I believe that this has also been the case in the game against England.
"I would like to say very clearly: since there were cases of racial discrimination in Sofia, I would like to sincerely apologise to the English footballers and to all those who felt offended.
"At the same time, however, I would like to address everyone who uses hateful language on social media, that my words have been incorrectly removed from context - and if that does not stop, I will be forced to take legal action against it."