Supporters and opponents of Armenian Prime Minister Nikol Pashinyan were to hold rival rallies in the capital Yerevan Monday amid a deepening political crisis over last year's war with Azerbaijan.

Pashinyan is under increasing pressure from the opposition for his handling of the war over the disputed Nagorno-Karabakh region, which saw Armenia suffer heavy losses and agree to hand over swathes of territory to Azerbaijan.

The prime minister last week accused the military of attempting a coup after the general staff called for his resignation, and the opposition has held a series of rallies in recent days demanding he step down.

The political uncertainty is threatening to set off a chaotic power struggle in Armenia, an impoverished ex-Soviet republic on the borders of Turkey and Iran.

Pashinyan, who came to power spearheading peaceful protests in 2018, has urged his supporters to gather from 6:30 pm (1430 GMT) on Monday in the capital's Republic Square.

"We must confirm the readiness of our people to support the democratic and consitutional system and the rule of the people," Pashinyan said during a broadcast on Facebook on Sunday.

He called the rally to coincide with the anniversary of the deaths of 10 people when riot police dispersed thousands of protesters contesting the result of a presidential election on March 1, 2008.

"There will be no new March 1sts in Armenia," Pashinyan said. "Regardless of our political views and positions, we are all brothers and sisters."

The head of his My Step faction that holds a majority in parliament, Lilit Makunts, told journalists it was "ready to take practical steps to hold snap parliamentary polls" and willing to discuss it with government critics.

The opposition has called its own rally for 6:00 pm in another part of Yerevan to press for Pashinyan to step down. 

Standoff over military chief

Anti-government protesters have held regular demonstrations since the military made its statement last Thursday and have set up a protest camp outside the country's parliament.

A small group of supporters of the opposition Dashnaktsutyun party entered a government building and held a demonstration inside on Monday but police stood by and they left without incident.

President Armen Sarkisian, whose role is largely symbolic, called for all sides to show restraint on the anniversary of the March 1 deaths.

"Political struggle must not go beyond the bounds of the law, it should not lead to shocks and instability," he said in a statement.

Sarkisian has become a central figure in the crisis after he refused on Saturday to sign an order from Pashinyan to dismiss the chief of the general staff Onik Gasparyan.

Pashinyan has sent the request for his dismissal back to the president and the two appear to be in a standoff.

The military has made no apparent moves against Pashinyan despite his warning of a coup after the general staff backed calls for him to step down.

Pashinyan has faced fierce criticism since he signed a Moscow-brokered peace deal over Nagorno-Karabakh, an ethnic Armenian region that broke from Azerbaijan's control during a war in the early 1990s.

Fresh fighting broke out over the disputed territory in late September, with Baku's forces backed by ally Turkey making steady gains.

After six weeks of clashes and bombardments that claimed around 6,000 lives, a ceasefire agreement was signed that handed over significant territory to Azerbaijan and allowed for the deployment of Russian peacekeepers.

The agreement was seen as a national humiliation for many in Armenia, but Pashinyan has said he had no choice but to agree or see his country's forces suffer even bigger losses.