At least 50 people, including 25 police officers, were wounded in Armenia after a night of clashes between police and protests linked to a four-day hostage standoff, the country's health ministry said.
Police said 136 people had been detained during Wednesday's violence in the capital, Yerevan, local journalist Roubina Margossian told Al Jazeera.
Demonstrators reportedly attacked police deployed outside a station where gunmen have been holding four officers hostage since Sunday morning.
The gunmen have demanded the resignation of President Serzh Sarkisian and the release of Jirair Sefilian, a jailed opposition leader and former military commander, who was arrested in June, according to AFP news agency.
Armenian news agency Civilnet identified the attackers as being members of the Daredevils of Sassoun, who also reportedly called for their supporters to take to the streets after the hostage-taking.
Their hostages include Armenia's deputy police chief General Major Vardan Egiazaryan and Yerevan deputy police chief Colonel Valeri Osipyan.
The demonstrations continued into the early hours of Thursday as some 2,000 protesters built barricades in front of the cordons of riot police, who responded with beatings and arresting scores of demonstrators.
"The situation escalated at 10pm and the clashes lasted between 30 to 45 minutes," Margossian, a journalist with Civilnet, said.
"Protesters started throwing water bottles at the police. The police threw them back and followed with stun grenades and tear gas," said Margossian, who was present during the clashes.
Opposition politician Nikol Pashinyan was reportedly at the scene of the clashes and tried to negotiate with both sides to stop the violence.
"He told the press that the police were intentionally escalating the situation in order to block off more territory and push the protesters out of the area," Margossian said.
When the gunmen seized the police regiment building in Yerevan's Erebuni district on Sunday, they killed one officer and took several captive.
They freed four hostages on Sunday and Monday, but were still holding four officers as of Wednesday night.
Clashes have been taking place since the night of the police station takeover on the 17th.
"While the crisis began as a criminal act by a small, radical and fringe opposition group with little popular support, the incident has sparked a deeper and more divisive confrontation driven by a combination of serious discontent within the country and a sense of accumulated frustration with an unpopular government," Richard Giragosian, director of Armenia's Regional Studies Center, told Al Jazeera.
Human Rights House Yerevan said in a statement: "During July 17 Armenian police detained more than 140 people in Yerevan, Gyumri and Vanadzor, including at least one minor."
The group said it "condemns the activities of the police against peaceful civilians on the 17th and 18th of July: in particular illegal detention, torture, keeping more than three hours without defining the status, in places not supposed for detention".
Many protesters were beaten and held without food and water for hours after being taken to police regiments not designed as detention centres, human rights activist Zara Hovhannisyan told Al Jazeera.
Sefilian, the leader of a small opposition group named the New Armenia Public Salvation Front, and six of his supporters were arrested in June after authorities said they were preparing to seize government buildings and telecoms facilities.
Sefilian has been critical of the government's role in the Nagorno-Karabakh region, where pro-Armenian separatists are engaged in a long-running conflict. An ethnic-Armenian, he was born in Lebanon where he fought in the civil war in the 1980s, defending Beirut's Armenian Quarters.
He then moved to Armenia to take part in the 1990s war with neighbouring Azerbaijan for control of the region of Nagorno-Karabakh.
Nagorno-Karabakh is an area in Azerbaijan but holds an ethnic Armenian majority.
Additional reporting from Anna Nigmatulina.