Authorities say 94 percent of those Armenian voters who cast their ballots on 27 November supported the legal changes proposed by President Robert Kocharian. But the opposition has accused the government of rigging the vote and harassing its election observers.
Hundreds of opposition protesters gathered near the Materadaran building, Yerevan's library of ancient manuscripts.
The demonstrators called on President Robert Kocharian to step down and vowed to keep pressure on the government so that the constitutional changes are not signed into law.
RFE/RL's Armenian Service correspondent Karine Kalantarian reported that the number of protesters has significantly dwindled compared to yesterday's demonstration. She said law-enforcement officers were visible everywhere, but there were no reported incidents.
Former Prime Minister Aram Sargsian, now a leader of the Justice (Atarutyun) opposition parliamentary group, told the cheering crowd that opposition parties have approved a resolution giving Kocharian's government until 2 December to annul the outcome of the referendum, or face further street protests.
Sargsian also cautioned the authorities against triggering a revolution similar to those that took place in Georgia and Ukraine in the past two years.
He said: "We will have the most civilized revolution possible. The government is forcing us to take these kind of steps. We will settle this problem through political means and achieve victory through peaceful means."
The Central Election Commission on 29 November released the final results of the referendum. They show 94 percent of those voters who cast their ballots supported the proposed changes.
Armenia's Arminfo news agency has reported that only seven of the Central Election Commission's nine members endorsed the results. It also quoted Feliks Khachatrian, an opposition representative in the election commission, as saying that no less than 1 million votes have been falsified.
The opposition has also questioned the 65-percent turnout figure given by the authorities. Observers from the Council of Europe have cast doubt on the turnout figures, saying they did not correspond with the "extremely low voting activity" they noted on referendum day.
The U.S. State Department's Bureau of European and Eurasian Affairs expressed similar concerns in a statement released on 29 November.
The statement, which was posted on the website of the U.S. Embassy in Yerevan, calls upon the Armenian government "to investigate Council of Europe observer reports of serious abuses and fraud."
Enhanced Parliamentary Powers
The U.S. State Department, however, has said it recognizes the substance of the provisions considered by voters in the referendum "as potentially strengthening democratic institutions in Armenia."
The proposed constitutional changes aim at curbing the powers of the president and enhancing those of both the parliament and the government. They are also designed to strengthen the power of the judiciary.
The international community has backed the proposals, saying they are essential to Armenia's future democratic development.
But the opposition, which claims Kocharian first came to power in 1998 through rigged elections, says the Armenian president has no legitimacy to modify the constitution.
Kocharian's opponents had called upon Armenian voters to boycott the referendum. But they also sent observers to monitor the vote.
Armenia's A 1 Plus independent news agency quoted the Anrapetutsiun (Republic) opposition party on 29 November as saying at least four of its election observers in the central city of Ashtarak were summoned to police headquarters for questioning today.
Meanwhile, the Armenian president has congratulated his fellow citizens on the adoption of the constitutional changes.
In a written message to the nation, Kocharian has called the vote "a great victory in the strengthening of democracy and the making of civil society in Armenia."