Armenians were voting on December 6 on a referendum about a government-backed proposal to switch from a presidential to a parliamentary form of government.
The government scheduled the referendum after President Serzh Sarkisian proposed the constitutional amendments, arguing the changes would "make cooperation between different branches of government more effective" and facilitate economic development and the protection of human rights.
The Armenian National Congress (HAK) and other opposition groups have been campaigning against the reforms, saying they are an effort by Sarkisian to remain in power after his final presidential term ends in 2018.
Sarkisian has refused to rule out that he would seek to become prime minister or speaker of parliament if the amendments are adopted.
He declined to answer reporters' questions after casting his ballot on December 6, saying that he will "answer all questions after the election."
HAK official Levon Zurabian said on December 4 that most Armenians oppose the amendments and that the government will not be able to win the referendum without falsifying its results.
With reporting by TASS