MADRID -- Spanish authorities are investigating the deaths of seven individuals believed to be linked to a widespread power outage that affected Spain and Portugal on Monday.

The fatalities occurred under different circumstances, all potentially connected to the blackout.

On Tuesday, members of Spain's Civil Guard discovered the bodies of an elderly couple, aged 81 and 77, and their 56-year-old son at their home in Taboadela, a town in the northwestern region of Galicia. Authorities suspect the trio succumbed to carbon monoxide poisoning caused by fumes from a generator placed outside their home. One of the victims reportedly had respiratory issues and sometimes required breathing assistance.

In a separate incident, a 52-year-old man died in Madrid's Carabanchel neighborhood following a fire in an apartment block around 10 pm (2000 GMT) on Monday. Thirteen others were treated for smoke inhalation. The fire is believed to have been started by a candle used for illumination during the blackout.

Three additional deaths, indirectly linked to the outage, occurred on Monday in Galicia. In Ferrol, a 59-year-old man with pre-existing medical conditions was found dead. An 80-year-old man died in Betanzos, while an 86-year-old man died in Dumbria.

The national power failure occurred on Monday at noon, with the cause still under investigation. Prime Minister Pedro Sanchez has pledged a thorough investigation to determine the cause and to prevent future incidents.