Yerevan (AFP) - Some 4,000 people rallied in Armenia's capital Yerevan on Monday to protest against constitutional reforms to curb presidential powers adopted in a controversial referendum.
"Take to the streets, be part of a revolution!" the marchers shouted into megaphones, calling on Yerevan residents to join the demonstration, according to an AFP journalist at the scene.
Protesters then filled Yerevan's central Freedom Square, vowing to hold permanent rallies until snap presidential and parliamentary polls are called.
Around two thirds (63 percent) of voters backed changes to the constitution to make the president a ceremonial figurehead, elected by parliament for a term of seven years instead of the current five.
The pro-Moscow government said the changes were needed to shake up the political system and strengthen democracy in the former Soviet state.
But the opposition believes the real aim was to keep President Serzh Sarkisian, 61, in power after his second term ends in 2018.
"We will not let Serzh Sarkisian to revel in power which he stole from the people," opposition MP Aram Manukyan, told the drum-beating crowd.
Ahead of the referendum, Sarkisian refused to repeat his earlier pledge not to run for any government office after his second and last term as president expires and defended his initiative, saying it will empower the opposition.
- 'Unprecedented violations' -
Council of Europe observers said Sunday's referendum was marred by allegations of large-scale vote buying and multiple voting, among other irregularities.
They urged the authorities to "address these issues in order to build trust in the voting process and in politics in general to ensure a genuinely democratic future for Armenia."
"Too many citizens" saw the reforms as "a means for the current president to remain in power," charged the observers.
The opposition also complained of widespread violations at polling stations and called on Armenians to take to the streets.
An umbrella group of local monitors said their observers noted an "unprecedented number of violations of the electoral law and international standards."
The Armenian National Congress opposition party of former president Levon Ter-Petrosian boycotted a parliamentary session on Monday to protest against the alleged "falsification of the referendum results."
And a top opposition leader, Raffi Hovannisyan, called on the president and prime minister to resign.
"What happened today is state treason," he told supporters at a small rally in the early hours of Monday.
Prime Minister Ovik Abrahamyan promised that the "alleged electoral irregularities will be investigated and -- if confirmed -- those responsible will be prosecuted."
A shrewd former military officer, Sarkisian, 61, has been in charge of the small landlocked nation of 2.9 million since winning a vote in 2008.
After that poll, 10 people died in bloody clashes between police and supporters of the defeated opposition candidate.
Sarkisian won a second term in 2013.
Earlier this year, brief protests erupted over electricity price hikes in the poor country, which has been badly hit by an economic crisis in Russia.