"What we are experiencing here does not happen by chance, this was provoked," he said after observing a minute's silence for the victims in the town of Pazos de Borben.
Hundreds of firefighters backed by water-dropping helicopters and planes battled 19 large wildfires in Galicia on Monday, the regional government said in a statement.
"Galicia is not burning by itself. Galicia is being burned," said Alberto Nuñez Feijoo, head of the regional government, blaming "terrorist arsonists".
Five wildfires near Vigo, Galicia's biggest city, forced the evacuation of a shopping mall and a Peugeot Citroen car factory on the outskirts of the city, though workers were able to return to the factory on Monday.
The city of around 300,000 residents has opened up two sports centres and booked rooms in three hotels for people who had to evacuate their homes.
Two women died on Sunday after being engulfed in flames trapped in their van near Nigran, outside Vigo, and an elderly man died in an animal shed near his house in Carballeda de Avia. Later on Monday it was confirmed that the fires had claimed a fourth victim, a man in his 70s who fell from an embankment while trying to battle a fire approaching his and a neighbour's house in Vigo.
Hurricane Ophelia swept past Spain before being downgraded to a violent storm on Monday as it battered Ireland.
Meteorologists said Ophelia was the most powerful hurricane recorded so far east in the Atlantic and the first since 1939 to travel so far north.
Galician authorities have declared three days of regional mourning.