Teams made up of firefighters and more than 3,500 forest workers, backed up by 30 aircraft, were battling 56 blazes in the worst hit northwestern region of Galicia while a further 40 were regarded as being under control.

Also affected, though to a far lesser degree, was the eastern region of Catalonia.

After Galician regional president Emilio Perez Tourino asserted Monday that "the majority (of the fires) are caused by criminal means", Spanish Environment Minister Cristina Narbona on Tuesday dubbed the fires "forestry terrorism".

She said she suspected some forestry workers had set fire to tinder dry land in anger at not being employed as auxiliaries over the summer by regional firefighting units.

Local officials have also cited "conflicts between ranchers and sheep farmers and landowners" over increasing grazing space and "behavioural problems" as further causes.

Following a similar spate of fires last year believed linked to property speculation -- a sector undergoing a huge boom in Spain -- the government passed a law banning immediate rebuilding on land devastated by fire.

Local Galician authorities meanwhile announced that two suspected arsonists had been arrested while one of three others arrested overnight Monday was released.

Of the first two, one was caught setting a blaze and the other turned in by his neighbours for suspicious behaviour.

The mayor of the worst hit zone of Pontevedra, Miguel Anxo Fernandez Lobec, told Cadena Ser radio he was "encouraging citizens to denounce the arsonists."

The Galician rural environment department said earlier that "we cannot rule out that there is an organisation behind all this," explaining the deployment of the anti-organised crime unit.

The blazes in Galicia, several of them raging within metres (yards) of residential areas, have come within two kilometres (1.2 miles) of the famous city of Santiago de Compostela, the end point of an historic pilgrimage trail.

The fires nearest the historic centre had been extinguished by Tuesday afternoon.

Three people have died in the fires -- two engulfed as they tried to flee in their car and a pensioner who tried to douse the flames near his home.

Spain's armed forces have been deployed to help coordinate civil protection, including evacuations, and prevent fires being lit.

In neighbouring Portugal 10 forest and brush fires were burning nationwide Tuesday, battled by 900 firefighters backed by 300 vehicles, six of them out of control.

The most serious was that at Valongo, near the northern city of Porto, where wind-fanned flames were advancing on two fronts. Some 300 men with 100 vehicles and a helicopter dropping water were combatting the fire.

Another fire, at Estremoz in the southern Evora district, was reported under control, though rising temperatures and low humdity meant that it could break out again, authorities said.

Police are investigating the possibility that the blaze, which has ravaged some 4,000 hectares (10,000 acres) of eucalyptus forests, was started deliberately.

So far this year 17 people have been arrested in Portugal for starting fires.

The country is on maximum alert until Friday because of the heatwave.

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