Bulgarian authorities have not only failed to counter the climate of intolerance, but "have actively engaged in inflammatory speech and at times openly encouraged violence," John Dalhuisen, Amnesty International's Europe Director, has said.

His words follow the attack on Krasimir Kanev, who heads the Bulgarian Helsinki Committee on Friday.

Kanev said on Thursday punched in the face and stomach by two strangers in the morning as he had been passing by a Sofia hotel near Parliament.

He told private NOVA TV station the next day that he had been targeted with insults and threats at least ten times since 2014.

"Today's attack on Krasimir Kanev is an alarming assault [on] one of Bulgaria's most respected human rights campaigners. Authorities must promptly investigate the incident and bring the perpetrators to justice in fair trials," also says.

He has added the attack comes at a time of increasing "xenophobia and intolerance directed against refugees, asylum-seekers and minorities including Roma as well as those who speak on their behalf".

The BHC has actively campaigned for the human rights of refugees and migrants, the Muslim population, Roma people and other ethnic, religious and sexual minorities.

The Balkan Investigative Reporting Network (BIRN) quotes him as saying attacks on him should partly be blamed on the fact that "the patriots are in power".

The Patriotic Front is a nationalist coalition which backs Bulgaria's minority government assuring it a parliamentary majority, but has no ministers in the cabinet.

It is not known who the attackers were as police arrived around 15 minutes after the incident.