Three seniors have died overnight after fire broke out in their room in the assisted living home they resided at in southeastern Bulgarian city of Haskovo.

According to preliminary police and fire service investigations, the three elderly men have passed away from suffocation.

The fire is believed to have started from a cigarette one of the residents left inextinguished while falling asleep.

The residence's management claimed that no major fire had started, as a nurse promptly put down the flames upon uncovering them.

The three old people however had already died, as insulated windows did not allow any ventilation from the smoke, said Haskovo mayor Georgi Ivanov.

The three men who perished are aged 67, 70 and 82. The man who is believed to have caused the fire is said to suffer from Parkinson's disease.

The tragic incident happened around 4.20 am Wednesday in the Kenana Park assisted living home in Haskovo.

Authorities found out that there is no fire warning system in the residence. Investigations are under way.