Censor.NET reports citing Radio Liberty.
The National Security Service said that a police officer was killed and two others were wounded in the shootout that occurred on early Sunday morning, July 17.
The opposition group Founding Parliament issued a statement demanding the release of group's leader Zhirayr Sefilian, a fierce government critic who was arrested last month.
Varuzhan Avetisian, a spokesman for the group, has also announced that "they are starting a rebellion" and an attempt to "overthrow the government" and "release political prisoners."
The NSS statement said that law enforcement agencies were functioning as normal to uphold public safety.
According to Shahnazaryan, the invaders have many weapons, they are bullet-proof vests.
Sefilian and six of his supporters were arrested on June 20 after the authorities initially said they were preparing a plot to seize several government buildings and telecommunication facilities in Yerevan.
Just days before his arrest, Sefilian announced plans to set up a new opposition movement called the National Resistance Committee. He said the new movement would try to topple the government "with the help of the people and the army."