Bulgaria coach Krasimir Balakov has apologised to the England team after fans taunted their black players with Nazi salutes and monkey chants during a Euro 2020 qualifier in Sofia on Monday.
England thrashed Bulgaria 6-0 to hand the hosts their heaviest ever home defeat but the game will be remembered more for the racist incidents that led to action being temporarily stopped in the first half.
European football's ruling body UEFA has opened disciplinary proceedings against Bulgaria over the racist behaviour.
While Balakov said after the game he had not heard any racist abuse from the stands, in an email to reporters late on Tuesday he apologised for the fans' behaviour.
"I strongly condemn and reject racism as a norm of conduct that contradicts modern human relations," Balakov said.
"This is a prejudice that comes from the past that must be eradicated forever.
"I want to say something very clear: given that there have been insults on such a basis, I, as a coach of the national team, apologise to the English footballers and all those who feel hurt."
Bulgarian Football Union President Borislav Mihaylov resigned on Tuesday, a few hours after the Balkan country's Prime Minister Boyko Borissov called for the former international goalkeeper to step down.
Mihaylov had previously defended Bulgarian soccer from accusations of racism and criticised England for what he saw as a "fixation" on potential incidents that could raise tension.
Meanwhile, Bulgarian police said on Wednesday they had detained six people in connection with the racist abuse, with more arrests likely.
"Six people were detained so far and we're searching for three more as we have collected evidence about their involvement in the incidents" Senior Commissioner Georgi Hadzhiev, director of the Sofia police department, said.
Hadzhiev added that the operation was still underway and they were trying to identify more suspects.