Thousands of incensed Armenians, most of them young, swarmed through Republic Square starting on April 13. The protests gradually spread to other major cities in the tiny southern Caucasus nation, including Gyumri and Vanadzor.

The pressure on Sargsyan, 63, to resign ratcheted up markedly on Monday after soldiers from one company of the country's prestigious peacekeeping force, which had served abroad in Iraq, Afghanistan and Kosovo, joined the march in Yerevan in their uniforms.

Tuesday is Armenia's Genocide Memorial Day, when many of the country's more than 2.6 million people turn out onto the streets. It was expected to quickly turn into a vast anti-Sargsysan demonstration that would have been unthinkable to suppress by force, said Aleksandr Iskandaryan, the director of the Caucasus Institute in Yerevan.

Sargsyan had promised last year not to try to extend his tenure in office by becoming prime minister when his presidential term ended.

Karen Karapetyan, who had just left the post of prime minister to make way for Sargsyan, stepped back in as acting PM.

The rapid events threw the country into disarray. The new constitution invests considerable power in the Parliament, and some expected snap elections to be called.

The demonstrations were fuelled by a new generation of Armenians disenchanted with the small elite of politicians and their oligarch allies who have long controlled the government and much of the economy, analysts said.

New York Times