Armenian police said protest leader Nikol Pashinyan was on Sunday "forcibly taken" from a protest rally, dismissing reports of his arrest as riot police and demonstrators clashed in Yerevan.
"Despite repeated calls to stop illegal rallies, Pashinyan continued leading a demonstration" in the capital, police said in a statement, adding that he and two other opposition MPs "were forcibly taken from the site" as riot police dispersed the rally.
An opposition MP Sasun Mikaelyan earlier told journalists that Pashinyan was arrested.
"People must liberate Nikol," he said.
As an MP, Pashinyan is protected by a parliamentary immunity and cannot be arrested without the approval of lawmakers, in accordance with the Armenian constitution.
Riot police using stun grenades clashed with demonstrators at the march led by Pashinyan in Yerevan's suburban district of Erebuni.
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It came shortly after new Armenian Prime Minister Serzh Sarkisian walked out of talks with the protest leader.
The televised meeting between the two only lasted for a couple of minutes on Sunday morning before the premier walked out, accusing the opposition of "blackmail".
Pashinyan had earlier announced the "start of a peaceful velvet revolution" in the landlocked South Caucasus nation of 2.9 million people.
Heeding a call from Pashinyan, protesters held rallies over the last 10 days to denounce Sarkisian's shift to the post of prime minister after a decade serving as president.
Opposition supporters have criticised the 63-year-old leader over poverty, corruption and the influence of powerful oligarchs.
Under a new parliamentary system of government, lawmakers elected him as prime minister last week.
Constitutional amendments approved in 2015 have transferred power from the presidency to the premiership.
After Sarkisian was first elected in 2008, 10 people died and hundreds were injured in bloody post-election clashes between police and supporters of the defeated opposition candidate.