Armenians protest to urge the government to respond to the Azerbaijani military operation launched against the breakaway Nagorno-Karabakh region outside the government building in central Yerevan on September 19, 2023. AFP
Armenia's opposition has accused Pashinyan of being weak on Karabakh, a region mostly populated by ethnic Armenians over which Yerevan and Baku have been locked in a dispute over decades.
"We must not allow certain people, certain forces to deal a blow to the Armenian state," Pashinyan said in a televised address.
"There are already calls, coming from different places, to stage a coup in Armenia."
Television and social media videos showed hundreds of protesters gathering outside government buildings in Yerevan, responding to a call by opposition parties to take to the streets.
Pashinyan has faced large protests in Armenia since losing swathes of territory to Azerbaijan in a 2020 war.
Opposition parties accuse him of making too many concessions on Karabakh.
He also faced protests during a blockade of the Lachin corridor, Armenia's only land link to Azerbaijan, that ended this week.
Pashinyan was elected after leading a peaceful revolution in Armenia in 2018.