A fire which since Tuesday has destroyed 2,700 hectares (6,690 acres) of pinewood and brush around the town of La Motte in the hard-hit Var department was still burning but was no longer advancing, officials said. A heavy rainstorm in the afternoon came as a major relief.

To the west in the Bouches-du-Rhone department, a fire which broke out Wednesday near Salon-de-Provence, 30 kilometres (20 miles) from the port city of Marseille, was brought under control during the night. The fire destroyed 500 hectares of woodland and seriously injured two firemen.

But later in the afternoon, some 180 firefighters were mobilised to extinguish a new fire near Rognac, also in Bouches-du-Rhone. The A7 motorway and a railway line were closed as a precaution.

Five people were killed, thousands evacuated from homes and campsites and 30,000 hectares destroyed in the devastating fires that swept through parts of southern France and the Mediterranean island of Corsica on Monday, amid the region's worst drought in a quarter of a century.

Despite the relative lull Thursday, temperatures remained high and forecasters predicted that the Mistral wind would pick up to speeds of around 60 kilometres per hour, creating perfect conditions for more outbreaks.

Exhausted firefighters remained on permanent standby with reinforcements sent in from other parts of France. Extra water-dropping planes have been sent from Greece and Italy, and more aircraft have been promised from Russia, Germany and Norway after a request sent by Paris via the European Union.

Suspicions that many of the fires may have been started deliberately were strengthened with the detention of several suspects in the region.

A 15-year-old was being questioned near Marseille after being seen acting suspiciously at the scene of a fire, and two boys were placed under judicial investigation after being spotted near Beziers to the west fleeing a fire on bicycles.

A 30-year-old municipal employee from the Var department, Stephane Jousse, was also placed under investigation Wednesday for arson after admitting starting several forest fires in July -- though not this week's deadly blazes.

Arrested on Monday, Jousse was being held at the medical wing of a prison in Marseille as he underwent psychological tests. Police said he was aggrieved after failing to be taken on as a volunteer fireman.

"He was always the first on the scene and the first to offer help to the emergency services," an official said.

Jousse faces a maximum penalty of 10 years in jail and a 150,000-euro (170,000-dollar) fine, though his lawyer said he would plead not guilty on grounds of diminished responsibility.

Another man spotted with a lighter in his hand was arrested in Florensac, in the Herault department.

French politicians have promised to take severe action against anyone caught starting forest fires, and identity checks have been introduced around high-risk areas to deter would-be arsonists.

"Those who continue to show criminal negligence or who deliberately light fires must know that the state will do all it can to find them and punish them, with all the severity demanded by the extreme gravity of their acts," President Jacques Chirac said during a cabinet meeting Thursday.

However local officials said most of the outbreaks were accidental, caused by cigarette ends, barbecues, sparks from machinery or even discarded bottles acting like magnifying glasses.

TERRA.WIRE