Opposition supporters claim last week's election was rigged in favor of the country's prime minister, Serge Sarkisian, and are demanding a new vote. As in previous days, the crowd protesting in a square in central Yerevan swelled to some 20,000 people in the afternoon, with hundreds breaking off to march around the city.

Hundreds of protesters have been staying overnight in tents.

The government in the former Soviet republic in the Caucasus mountains says Sarkisian won the presidency with nearly 53 percent of the vote Feb. 19 and has called on the protesters to disperse. Authorities have detained several allies of opposition candidate Levon Ter-Petrosian, who claims he was robbed of victory by election fraud.

Petros Makeian, a leading backer of Ter-Petrosian, was detained Monday, police said. Separately, the national anti-organized-crime police said they stopped a convoy of three vehicles in which Khachatur Sukiasian, a lawmaker with a business background who supports Ter-Petrosian, was traveling.

Guns, knives, bulletproof vests and ammunition were found in the vehicles and several bodyguards were detained, police said, but Sukiasian has immunity from prosecution as a parliament member and was not taken into custody.

Also Monday, two Ter-Petrosian supporters who held high-level posts when he was Armenia's president in the 1990s were placed under arrest on charges of violence against government authorities _ accusations that apparently stemmed from clashes that police say broke out when they were detained over the weekend.

Former Deputy Prosecutor-General Gagik Dzhangirian was detained Saturday and Smbat Aivazian, a tax collection agency chief during Ter-Petrosian's presidency, was detained Sunday. In both cases, police said weapons were found in their vehicles.

Another opposition figure, New Times party leader Aram Karapetian, was detained Sunday. He is accused of making false accusations against Sarkisian and President Robert Kocharian, and officers searched the party's office early Monday, confiscating computers, the National Security Service said.

Meanwhile, six more Foreign Ministry officials joined a handful of diplomats who announced their support for the opposition following the election, saying they were disturbed by violations. The diplomats have been fired from their posts.

Foreign Minister Vardan Oskanian expressed regret over the attrition but said the government was in control.

"The opposition has been unable to shake the foundations of state authority," Oskanian said after meeting with Slovakian Foreign Minister Jan Kubis. He called on both sides to show restraint and seek consensus but warned the opposition against seeking to take power by force.

The standoff has raised concerns about stability in the volatile, strategic country at the junction of the energy-rich Caspian Sea region and southern Europe, with Iran and Russia _ which has close ties and maintains a military base in Armenia _ nearby.

While the fraud claims have struck a chord with many Armenians, memories of severe economic hardships of the early 1990s and the devastating conflict with neighboring Azerbaijan over the territory of Nagorno-Karabakh are still fresh, and the desire for calm and stability runs deep.