The three men, who were among more than 1,000 firefighters battling the blazes, were on a firetruck that was suddenly encircled by flames in the Maures hills of the Var region, where massive forest fires had already claimed four lives in July.

They were burned alive, officials said, while three other firemen in a second truck that was also trapped in the flames managed to escape.

Hundreds of reinforcements were sent Tuesday morning to battle the blaze, whose two previous fronts had merged into a huge wall of fire overnight near Cogolin, where the three firemen were trapped and perished.

"There are now 1,600 men on the scene and we are expecting 400 more to arrive during the morning," regional fire chief Lieutenant-Colonel Jacques Baudot told AFP.

The dead firefighters, aged 37, 42 and 43, were all married and had seven children between them, aged one to 12. The rest of their company was sent back to the station house and were receiving psychological conselling, Baudot said.

President Jacques Chirac expressed "deep sadness" over the deaths. He hailed the courage of the "thousands of volunteers and professionals who have fought day and night for the last three months against the fires devastating the south of France and Corsica -- too many of them started deliberately".

Since Sunday, 12 firefighters have been either burned or injured fighting the fierce flames.

Several new blazes erupted early Monday but efforts to quench them were hampered by winds of up to 50 kilometers (30 miles) an hour.

Rescue workers evacuated 40 families from the town of La Garde-Freinet, as well as campsites in four areas -- Croix-Valmer, Gassin, Cavalaire and La Molle -- and a vacation resort in the Maures hills, northwest of Saint-Tropez.

Three helicopters and a boat were standing ready to evacuate firemen and civilians and a team of psychologists were on hand to help trauma victims, officials in the Var region said.

The regional authorities also announced that the resumption of school following the summer break had been postponed in seven towns around the Gulf of Saint Tropez.

They said this was in order "to avoid hindering emergency services" battling the fire, which doubled in size in the space of two hours Monday night and has now devastated around 4,500 hectares (nearly 10,000 acres).

Blazes in the same region killed four people -- including three foreign tourists -- in July amid a heat wave and the worst drought in southern France in a quarter of a century.

Forest fires also continued to blaze out of control on the Mediterranean island of Corsica, where 7,200 hectares of brush and pinewood had been consumed in the space of three days, the authorities said.

Most at risk was Cap Corse, the northernmost tip of the island, local officials said.

One person died in July in Corsica's fires, bringing the death toll from France's summer fires to five.

Interior Minister Nicolas Sarkozy said during a recent visit to fire-hit areas in southern France a total of 54,000 hectares of woodlands had been destroyed across the country thus far this year -- the worst total in 15 years.

TERRA.WIRE