MOSCOW — Police in St. Petersburg say they are searching for unidentified assailants who attempted to set fire to a building housing the studios of a director whose film about the last Russian czar’s affair with a ballerina has fueled controversy.

Police said no one was hurt in Thursday’s incident and the building suffered no damage except soot left on its facade, according to Interfax.

The building houses the studios of Alexei Uchitel, whose film “Matilda,” set for release in October, describes Nicholas II’s relationship with ballerina Matilda Kshesinskaya.

The film has drawn harsh criticism from some Orthodox believers and hard-line nationalists, who see it as blasphemy against the emperor, glorified as a saint by the Russian Orthodox Church. The campaign reflects the growing assertiveness of conservative activists.