The vast majority of the 19,000 wildfires that have raged across Spain this summer have been started by arsonists or are the result of human carelessness, according to the country's environment minister.

Cristina Narbona provoked controversy on Monday by saying fewer than one in 20 of this summer's blazes, which have killed more than a dozen fire fighters, could be attributed to "natural causes." The rest, about 18,000, had been started by people - including arsonists hoping to gain financially - who were later protected by a conspiracy of silence among their families, friends and neighbours.

"It is clear that there is tolerance and complicity," Narbona said. "There are people who start the fires, and others who tolerate them."

With only 277 suspected arsonists and people who set fires by accident so far arrested, Narbona said it was obvious the perpetrators were being hidden. This was especially so in small, tight-knit villages in Galicia, the north-western region which has accounted for 40 per cent of the fires. "It is naive to think that people act on their own," she said.

Newspaper reports have suggested those who benefit economically from fires include some forestry companies, developers wanting to build on green land, drugs smugglers trying to divert the attention of police, and people seeking insurance money.

Among the suspected arsonists arrested so far, at least one belongs to the groups of rural fire fighters that are employed on a day rate to put out wildfires.

Pablo Salazar, a columnist on the Las Provincias newspaper, said: "Everybody knows there are hidden motives behind the fire-setting, that the pyromaniacs are not madmen who operate on their own, and that there are businesses who are glad to see the countryside burn and mayors who dream of putting up rows of houses where there were once pine trees."

Spain has recently passed a law preventing town halls handing out licences for building on burnt land.

Police in neighbouring Portugal have announced that they will draw up a national database of pyromaniacs, after losing 180,000 hectares of forest and scrub to fires this year.

The wildfires have burnt 5 per cent of the country's forests and killed 14 people, in a year that has also seen a record-breaking drought.