The country's veteran leader Serzh Sarkisian stood down on Monday from his new post as prime minister after days of protests by demonstrators who accused him of a blatant power grab.
Pashinyan, the leader of the opposition movement, was due Wednesday to hold talks with acting head of government Karen Karapetyan to discuss a "peaceful" transfer of power but the talks were cancelled at the last minute, plunging the impoverished country of 2.9 million people into fresh turmoil.
Pashinyan said the ruling Republican Party did not wish to cede power and called on his supporters to renew protests.
"We can't allow the Republican Party to continue ruling the country," he said in a live video address Tuesday night.
"The problem was not only Serzh Sarkisian, but the entire Republican Party."
Karapetyan confirmed the planned negotiations had been cancelled and accused the protest leader of putting forward "new demands" concerning the proposed talks.
"This not a negotiation, a dialogue but simply promoting his own agenda," Karapetyan said in a statement.
He said he asked Armenia's President Armen Sarkisian, who is no relation to the former leader and is a ceremonial figurehead, to help organise talks with "the participation of a wider spectrum of both parliamentary and non-parliamentary political forces."
Earlier Tuesday Pashinyan, the 42-year-old leader of the Civil Contract party, told reporters he was ready to lead the Moscow-allied country.
The new prime minister must be a "people's candidate" and not a member of Sarkisian's ruling Republican Party, he said.
Last week Sarkisian was elected prime minister by lawmakers after serving a decade as president, triggering political turmoil in the South Caucasus country which is locked in a simmering territorial dispute with Azerbaijan.
The opposition charged that the 63-year-old wanted to extend his grip on power under a new parliamentary system of government, saying he failed to tackle a litany of problems such as poverty and corruption.
Protests broke out several days before his expected election, with tens of thousands of people eventually taking to the streets of Yerevan and other cities in largely peaceful protests.
Russia -- which has a military base in Armenia -- has appealed for stability but said it would not interfere.
Armenia's arch-foe Azerbaijan expressed the hope that new Armenian authorities would adopt a "constructive" approach over the breakaway region of Nagorny Karabakh.
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