The demonstrators said they were prepared to stay on the square to protest the referendum and the government of President Robert Kocharian and would set up tents on the square after the referendum.
Former Foreign Minister Raffi Hovanissian led the protest. On 25 Novmeber he told protesters the constitutional referendum was illegitimate.
Campaigning has already ended but, before it did, the opposition had called on voters to boycott the referendum.
Armenia's opposition originally told citizens to vote "no" on the referendum.
President Kocharian urged people to vote "yes" in the referendum saying it was not a vote for him, but for the country and its children.
RFE/RL Caucasus Report
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