Armenia's acting head of government Karen Karapetyan on Friday rebuffed talks proposed by opposition leader Nikol Pashinyan who says he is the only possible candidate for prime minister.
Karapetyan's refusal to negotiate came after he spoke to Russian President Vladimir Putin by phone Thursday.
The Moscow-allied ex-Soviet country has been in the grips of a political crisis over the past weeks, with veteran leader Serzh Sarkisian quitting after a decade in power.
Pashinyan on Thursday issued an ultimatum to the authorities, saying he should be elected prime minister in a vote by lawmakers on May 1.
"The acting prime minister believes that negotiations where one side dictates the agenda and the other cannot do so, cannot be considered negotiations," a spokesman for Karapetyan told AFP.
The move is expected to further escalate tensions in the impoverished nation of 2.9 million people.
"If I am not elected prime minister, then Armenia will not have a prime minister at all,", Pashinyan had told his supporters at a rally in the capital Yerevan on Thursday.
The 42-year-old former newspaper editor added he was willing to hold talks with Karapetyan with reporters present. A previous attempt at talks collapsed earlier this week.
The protest movement accuses Sarkisian's ruling Republican Party of clinging onto power after his rule failed to tackle widespread poverty, corruption and influential oligarchs close to the authorities.
The opposition says its candidate should be elected prime minister under a parliamentary system of government to clean up the political system.
But the ruling party has a majority of seats in parliament and Pashinyan does not have enough support from lawmakers to get elected.
On Thursday Pashinyan called a temporary halt to protests in Yerevan and urged his supporters to instead stage a rally in Gyumri, the country's second largest city north of the capital which hosts a Russian military base.
Another rally is planned for Saturday in the third largest city of Vanadzor.
Observers have warned the crisis could destabilise the South Caucasus nation, which has been involved in a decades-long territorial dispute with Azerbaijan.
A number of top Armenian officials held talks with Russian Foreign Minister Sergei Lavrov and other officials in Moscow on Thursday.
Accused of seeking to extend his grip on power after a decade serving as president, Sarkisian resigned this week after 10 days of opposition protests in which tens of thousands took to the streets.