Armed men seized a police station and hostages in Armenia's capital Yerevan on Sunday, demanding Armenians take to the streets to press their demands for the release of opposition politicians they said had been jailed unfairly.
One of their main demands was to free Jirair Sefilian, an opposition politician whom the authorities have accused of plotting civil unrest.
Sefilian was jailed in June over allegations of illegally possessing weapons.
Armenia's security service said one policeman had been killed and two wounded in the violence, but that negotiations were now underway to resolve the standoff peacefully, Reuters reported.
Two hostages had been freed, it said. Armenian news agencies cited police sources as saying seven or eight hostages remained.
Photographs from the scene show the area ringed with white armored vehicles.
Though far smaller in scale, suggestions by one opposition politician that an armed uprising was underway stoked speculation that the hostage-takers had drawn inspiration from an unsuccessful coup attempt in neighboring Turkey.
The security service accused the hostage-takers' supporters of spreading false rumors on the Internet about an uprising and the seizure of other buildings. Such assertions were pure "disinformation", it said.
"The National Security Service officially announces that such information is absolutely untrue," it said in a statement.