Bulgarian Football Union's (BFU) president Borislav Mihaylov has resigned following racist abuse and monkey chants from Bulgaria fans towards England players during their Euro 2020 qualifier.
Prime Minister Boyko Borissov had called for former goalkeeper Mihaylov to step down after the match, won 6-0 by England, was temporarily halted by the referee to tackle abuse from the crowd under a three-step protocol by European soccer governing body UEFA.
BFU spokesman Hristo Zapryanov earlier said that the president would not resign but Mihaylov, who was also a member of the UEFA executive committee, has decided to step down.
More than 20 police officers swept into the BFU headquarters in Sofia less than a hour after president Mihaylov's resignation.
"I can confirm the presence of police officers but I can't provide more details at the moment," a BFU spokeswoman told Reuters on Tuesday.
Sources close to the issue told Reuters that officers had been searching for documents related to some Bulgarian referees.
"I urge Borislav Mihaylov to immediately resign as president of the Bulgarian Football Union!" Prime Minister Borissov had posted on Facebook after the footage of Monday night's match was seen around the world on television and social media.
"It is unacceptable for Bulgaria, which is one of the most tolerant countries in the world, and people of different ethnicities and religions live in peace, to be associated with racism and xenophobia."
A group of black-clad Bulgarian fans, some of whom were making right-wing salutes, were moved from an area behind the dugout at the Vasil Levski national stadium with home team captain Ivelin Popov having tried to appeal to the supporters in a heated discussion at half time.
"[England] heard racist chanting in the first half and told the referee," he told NOVA TV. "I spoke a few times with the security in the South Stand, to try and stop them.
"We are affected by that. At the half time we spoke with the officials and England squad about whether to play the second half. Gareth Southgate thanked me because I tried to do something."
Winger Raheem Sterling backed the prime minister's call.
"A good move credits to you M. Borissov," the Manchester City striker wrote on Twitter.
Earlier, sports minister Krasen Kralev said the government would suspend relations with the BFU, including financial ties.
The BFU was not immediately available to comment. However, after Monday's match, they tried to play down the incidents.
"It's quite disappointing to focus on racism," BFU vice-president Yordan Lechkov said. "It's not serious to concentrate on that if there's a qualifier like this and we're playing against a team like England."
UEFA had ordered the BFU to partially close the Vasil Levski stadium for England's visit after supporters were found guilty of racist behaviour in matches earlier this year.
Racist chanting was heard from the stands and reported by England players to Southgate, with the referee informed and a public announcement made on two occasions.
Most of the Bulgaria players and their coach said after the match they had not heard any abuse of the visiting team.
Coach Krasimir Balakov said there had not been such racial incidents before and blamed England fans for being disrespectful to Bulgarian supporters.
"During the second half they used words against our fans which I find unacceptable," he said.
The BFU and a number of Bulgarian clubs have been fined by for racist abuse several times over the past few years.
Meanwhile, UEFA announced they have opened up disciplinary proceedings against both Bulgaria and England following the match.
The BFU are under investigation after Bulgaria supporters engaged in racist behaviour, threw objects and disrupted the national anthem, while there were also replays on the giant screen.
While the English Football Association are being investigated after supporters disrupted the national anthem and as there was an insufficient number of travelling stewards.