Russian police on Saturday detained two people, including the suspected perpetrator, after a fire killed at least 13 people at a bar in the historic city of Kostroma.

Russian emergency services told state television that 13 people were killed, denying earlier media reports that 15 people had died. 

Fire fighters fought through the early hours to extinguish the blaze at the popular Poligon bar in the city, which is around 300 kilometres (180 miles) northeast of Moscow.

Russian agencies reported that the fire could have started after a drunk man fired a "flare gun" on the dance floor.

"Police officers identified and detained the suspect (behind) unlawful acts in an entertainment establishment in the city of Kostroma, which resulted in a fire and the death of people," Russian police said.

Russia's Investigative Committee said he was aged 23. 

It later said a second person was detained, a woman who acted as an organisational director of the bar, in a criminal case on the failure to meet safety requirements.

The RIA Novosti news agency said the bar belonged to a local deputy of the ruling United Russia party, Ikhtiyar Mirzoyev.

Kostroma, a city on the Volga river of around 230,000 people, is one of Russia's oldest cities and famous for its medieval architecture and monasteries.

Authorities published images from inside the burnt-out building, showing the bar with a collapsed roof, burnt-out walls and near total destruction inside.

- 'Flare gun' -

State television aired night-time images of the bar -- housed in a single-storey logistical centre -- engulfed in flames.

Authorities said the fire started at around 2:00 am local time (2300 GMT Saturday) and was put out at around 7:30 am.

They declared an official mourning in the region for Monday. State flags would be lowered in the region and entertainment events cancelled, the regional administration announced. 

TASS news agency, citing emergency service sources, said a drunk man with a "flare gun" was likely to have caused the fire.  

"He was spending time in the bar with a woman, ordered her flowers, with a flare gun in his hands," the source told the agency.

"Then he went to the dance floor and fired it."

Emergency services said the blaze engulfed more than 3,500 square meters (37,700 square feet).

Around 250 people were evacuated from the building after it caught fire, authorities said.

Some local media, quoting witnesses, said here was panic when the fire started as people rushed to an exit, causing a jam. One man forced a closed door open, possibly saving lives, according to reports.

- Lax safety -

On its website, Poligon says it acts as an evening and night-time "place for recreation and entertainment".

By day, it is a typical Russian "stolovaya" -- a casual restaurant serving traditional food.

It says it is housed in a "distribution centre" and is popular with traffic police.  

State television showed images of dozens of emergency workers fighting the inferno.

The sign "Poligon" was visible amid the flames raging on its roof.

One fire fighter told state television that it took 50 people to extinguish the blaze and that they had used 20 fire engines.  

He said the fire was especially difficult to put out because of a risk that the building might collapse.

Russia, which frequently has a lax approach to safety rules, has seen a number of deadly fires at entertainment venues in recent years.

In 2018, a fire killed 60 people in a shopping mall in the Siberian city of Kemerovo.

In 2009, another blaze at a nightclub in the Urals city of Perm killed 156 people. 

bur/jm