The leaflets in Russian, French and English were signed by a previously unheard-of "Guamayun Union of Resistance Forces" and hit out at "the current dictatorial regime."
The Guamayun nationalists -- named after a mythical bird of Russian folklore -- had a few days earlier sent threatening letters by post to several Russian and foreign journalists in Moscow.
"The leaflets started to rain down from the balconies, the people below were covered in them," said spectator Natalia Miller after the ill-fated performance Monday of nationalist composer Mikhail Glinka's opera "Ivan Susanin."
The culprits fled the scene without being caught, a spokesman for the Federal Security Service, or FSB, said.
In its Russian version, the leaflet signed by the group denounced "the present dictatorial regime" and promised to "direct the anger of the people" against their leaders.
The French version of the leaflet, aimed at the large number of tourists in the audience, called on them to "demand that their governments stop supporting Russian tyranny."
The agitators chose a very patriotic opera at which to make their point. It tells the legend of the 17th-century peasant Susanin, who lured the occupying Polish army into the Russian swamps.
The version of the letter sent to foreign journalists accused them of misleading the international community by generating propaganda for the Russian regime.
"Russian patience also has limits. While they have not been attained, you still have time to tell the truth and to convince the world not to support Russian tyranny," concluded the message, which was addressed to bureau chiefs in several French, American and Spanish media organizations.
Several Russian media organizations, such as the liberal daily Segodnya, received similar threats, said Sergei Bogdanov, spokesman of the Moscow branch of the FSB.
The FSB believes this could be a publicity stunt. "This organization has never come to any notice, at least in Moscow. It seems it is a media stunt aimed at drawing attention to themselves," the spokesman added.
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