YEREVAN -- Gunmen affiliated with an Armenian opposition group have freed three of seven hostages at an occupied Yerevan police station as a standoff with security forces enters a second day.

The occupation started when at least a dozen gunmen stormed the station in the city’s southern Erebuni district at dawn on July 17, killing one police officer and wounding six other people.

The gunmen are demanding the release of Zhirayr Sefilian, the leader of the Founding Parliament opposition movement, who was arrested last month for allegedly plotting an armed revolt.

They also want President Serzh Sarkisian to step down.

The hostage takers and the police officers they are holding have reportedly been supplied with food and medication.

Earlier, a first deputy chief of the Armenian national police force, General Hunan Poghosian, told reporters that those still being held include two senior police commanders.

Their releases were part of ongoing negotiations, the National Security Service (NSS) said in a statement.

The officer killed during the storming of the station was named as a police colonel, Artur Vanoyan.

The Armenian Health Ministry on July 18 raised the casualty figure from four to six injured.

Aravot.am reported that one of the gunmen told the website by telephone that the group had freed the first two hostages at Sefilian's request, relayed to them by another Founding Parliament member who was allowed to visit them late on July 17.

But he added that negotiations would continue for the time being.

Varuzhan Avetisian, a spokesman for Founding Parliament, announced that "they are starting a rebellion" and an attempt to “overthrow the government” while also trying to secure the "release of political prisoners."

The group has released a video on Facebook calling on Armenian citizens to take to the streets against the government.

The Facebook video showed several men in flak jackets and armed with Kalashnikovs as well as several hostages being held inside the police building.

"We are doing this for you. People, take to the streets!" one of the gunmen said in the video while also calling for the release “of all political prisoners."

WATCH: Armed Attackers Storm Yerevan Police Headquarters

The gunmen's call for public unrest reportedly has met with silence.

Police have cordoned off the area near the police station, with armored vehicles blocking off the road to the police station.

“The law-enforcement agencies fully control the situation and are taking all necessary measures to resolve it,” the NSS said in a statement.

President Serzh Sarkisian held consultations with security officials to decide how best to handle the situation, his office said, saying he had been told that the siege was completely under control.

Residents of nearby apartment buildings said they heard several explosions early in the morning and gunshots were also reported afterwards.

Meanwhile, opposition lawmaker and outspoken government critic Nikol Pashinian visited the police station and spoke with the attackers twice during the night.

Pashinian, the leader of the newly established Civic Agreement opposition party, said one of the attackers inside the police station had a serious head wound.

He also said a policeman, who was feeling unwell, was released by the hostage-takers.

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The Founding Parliament group frequently stages street protests in Yerevan demanding Sarkisian's resignation.

The group is particularly critical of the way the government has been handling a long-running conflict in Azerbaijan's breakaway region of Nagorno-Karabakh, the territory claimed by both Armenia and Azerbaijan.

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.

He was formally charged with illegal acquisition and possession of weapons. Sefilian says the case against him is politically motivated.

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.”

Sefilian was arrested in 2006 over calls for "a violent overthrow of the government."

He was released in 2008.

In 2015, Sefilian was arrested again along with several of his supporters on suspicion of preparing a coup, but released shortly afterwards.

With reporting by AFP and AP