They are loudly voicing their belief that former President Levon Ter-Petrossian, who finished second in the February 19 poll, lost only because the election was rigged.
Ter-Petrossian has vowed to file a complaint with the Constitutional Court, and is demanding that a new vote be held.
The protests have gained momentum in recent days, with several government officials coming out in support of the opposition. Many of them, including nine high-ranking Foreign Ministry officials, have reportedly resigned.
In the last few days, several key opposition activists were arrested in separate incidents. Among those arrested were the leader of one political party and a former deputy prosecutor-general.
Fears were raised that the authorities might resort to force to break up the peaceful protest after outgoing President Robert Kocharian held a meeting on February 23 with top military and security officials. He described the opposition protests as an "attempt to seize power by illegal means" and said that "law and order" was to be enforced.
His instructions were followed up with the detention of the opposition figures on February 23-24 and with the deployment of a large police presence in central Yerevan on February 24.
On February 23, police detained former Deputy Prosecutor-General Gagik Jahangirian, who had resigned in protest a day earlier. Gunfire was reportedly exchanged after officers stopped the vehicle in which Jahangirian was traveling, and authorities said a search of the vehicle uncovered four pistols and a hunting rifle.
The next day, police detained Aram Karapetian, leader of the opposition party New Times, and politician Sambat Ayvazian, a former tax chief.
Armenian officials said both Ayvazian and Karapetian were detained for possessing illegal weapons. The New Times' offices were subsequently searched and computers confiscated, according to RFE/RL's Armenian Service.
RFE/RL's Armenian Service reported that Petros Makeyan, chairman of the opposition Democratic Homeland party, was detained early on February 25. The circumstances of his detention are unclear.
"I would evaluate the situation very negatively," says Mikael Danielian, chairman of the Armenian Helsinki Association. "Even though the authorities are not resorting to wide use of force, these permanent arrests of Levon Ter-Petrossian's supporters -- which sometimes look like kidnappings, with the detainees allowed to meet their lawyers only the following day -- all this indicates that the authorities are trying to stifle the movement, by use of force."
RFE/RL Caucasus analyst Liz Fuller says the recent detentions may be part of the outgoing president's attempts to tie the protests to a conspiracy plot.
If the allegations of illegal weapons possession "are not true, then they are clearly intended to substantiate Robert Kocharian's allegations, when he met with police and army commanders on Saturday that Ter-Petrossian is plotting to seize power by illegal means, the implication being that he would not stop at violence," she says.
Ter-Petrossian has claimed that the arrests are politically motivated. "First of all, this is clearly political matter," he said. "Apart from this, I think the authorities are trying to frighten other state officials, so that they do not follow Jahangirian's example."
Among the nine Foreign Ministry officials who have resigned are Deputy Foreign Minister Armen Bayburtian, and the ambassadors to Italy (Ruben Shugarian) and Kazakhstan (Levon Khachatrian). A diplomat posted in Ukraine, Razmik Khumarian, and a ministry spokesman, Vladimir Karapetian, were also dismissed.
The opposition has vowed to make the protests a "permanent feature" in central Yerevan unless a new vote is held. But as analyst Fuller explains, the government seems willing to wait the situation out, believing it has the support of the international community.
"Serzh Sarkisian has a reputation as a gambler," she says. "One would therefore suspect that he has very, very strong nerves, and he is waiting for the other side to blink first. I suspect that Sarkisian and Kocharian are firmly convinced that the international community is on their side, and that if they simply wait, in a week, or two weeks -- or even longer -- the protests will fizzle out."
In its preliminary assessment, the Organization for Security and Cooperation in Europe's (OSCE) election-monitoring body, the Office for Democratic Institutions and Human Rights (ODIHR), has said the vote was "mostly in line with the country's international commitments, although further improvements are necessary."
The vote-counting process was assessed negatively at about 16 percent of the polling stations visited by ODIHR observers.
Nevertheless, the elections have been endorsed by the European Union and, while not congratulating Sarkisian personally, the U.S. State Department has congratulated the Armenian people on an "active" and "competitive" election, while also noting "significant problems with electoral procedures."
Sarkisian has received messages of congratulation on his election win from the presidents of Russia, France, Georgia, and Turkey.