MOSCOW — Street demonstrations resumed in the Armenian capital of Yerevan on Wednesday at the urging of an opposition leader, after negotiations stalled on the way forward after the unexpected resignation of the prime minister.

The resumption of public protests and the deployment of the police around the headquarters of the ruling Republican Party threatened to shift the tenor of what has so far been a peaceful movement for change in the small, southern Caucasus nation of about three million people.

Nikol Pashinyan, 42, a member of Parliament and the leader of demonstrations that forced the resignation of the prime minister, Serzh Sargsyan, led the marchers, who beat drums and chanted for new elections. Local news agencies carried live feeds showing the protests.

Although Mr. Pashinyan lacks a party and an established constituency, he has won widespread support, mainly among young Armenians who are fed up with corruption and nepotism in the elite group of pro-Russia politicians and their allies who have long commanded the government and the economy.