The demonstrators denounced comments by the Russian President, Boris Yeltsin, that a recent agreement between Moscow and the former Soviet republics of Belarus, Kazakhstan and Kyrgyzstan could be expanded to include "other countries ... perhaps, for example, Bulgaria".
They also called on their own socialist-led government to issue an unequivocal rejection of Moscow's proposal and to re-confirm Bulgaria's essentially pro-Western orientation.
Valentin Vassilev, an MP from the opposition Union of Democratic Forces (UDF), said: "We have to make it clear that we do not want to get sucked into some sort of Soviet Union Mark II."
Last Friday's agreement between Russia, Belarus, Kazakhstan and Kyrgyzstan essentially concerned the strengthening of economic ties and was an important step towards Moscow's goal of achieving a rapprochement between the former Soviet republics. Yesterday, Russia and Belarus went considerably further, agreeing a bilateral treaty on closer political integration.
The singling out of Bulgaria as a potential future partner provoked uproar in Sofia, sparking speculation that the government - in the hands of what opponents perceive to be Moscow-friendly former communists - may have been involved in secret negotiations.
Government spokesmen have denied that a deal has been struck, but their criticisms of Mr Yeltsin's remarks have been noticeably muted.Reuse content