A man put a gas pistol to the head of the leader of Bulgaria's ethnic Turkish party during a televised conference.
Ahmed Dogan, leader of the Movement for Rights and Freedoms (MRF) was unharmed and the unidentified man was wrestled to the ground by security guards.
The incident happened on Saturday at a party congress in the capital Sofia.
Interior Minister Tsvetan Tsvetanov said the attacker, himself an ethnic Turk, tried to fire two shots but "most likely the gun misfired".
Early reports suggested the weapon was a gun, but it was later confirmed to be a gas pistol - a non-lethal weapon used largely for self-defence which does not fire bullets but which can cause serious injuries if fired from close range.
Mr Tsetanov also said the assailant had a criminal record for drugs possession, robberies and hooliganism.
Police arrested the attacker, a 25-year-old from the Black Sea town of Burgas, who was also carrying two knives.
The liberal MRF party represents ethnic Turks and other Muslims, who make up about 12% of Bulgaria's population of about seven million.
Mr Dogan, 58, has led the party for almost 25 years. He returned to the party conference a few hours after the attack and was given a standing ovation.
President Rosen Plevneliev said in a statement: "Bulgarian society is traditionally known for its tolerance, mutual acceptance and respect between different ethnic groups and religions.
"Such an act is unacceptable in a democratic state."
Attacks on politicians are rare in Bulgaria, but in 1996, former Prime Minister Andrei Lukanov was found shot dead near his home in Sofia.