The eastern Burmese region is now a front line of conflict and a black zone where anyone can be shot on sight. Just a few metres away from Burma, across the border in Thailand, a young refugee showed France 24 reporters the jungle he went through with his family to escape a massive Burmese army offensive and flee to Thailand.

Burmese soldiers are just a few dozen metres away. They are here because they have launched a surprise attack against ethnic Karen rebels.

On the Thai side, villages are empty. On the front line, France 24 found volunteers who are helping the arriving refugees.

Shelling could be heard while talking to the aid workers. Fighting has started again.

"They want to annihilate the Karens,” said a Western volunteer, who requested anonymity. “The world has to understand that this is just as bad as any Darfur or anything else. We just can’t see it happening. Except we can hear the sounds."

One kilometre away, there is the first shelter for hundreds of families who have just arrived in Thailand. Exhausted women and children have had to walk for more than a week through the jungle under torrential rains.

Many people in the camp have been wounded.

The Burmese army systematically attacks Karen villages on the suspicion that they support the guerillas.

The first victims of the conflict are civilians.

“I lost my leg when I stepped on a landmine,” said a man in the camp.

“More and more are arriving,” said Maung Maung, the shelter's leader. “They flee the fighting, but they are also afraid of being army prisoners and to be used as porters. The world has to help us to stop this war. These people must have the right to come back to their land and live in peace.”

All this vast border area is under threat.

An advance patrol of the Thai army has taken up position. They are monitoring the movements on the mountain. The fighting has spread dangerously to this side of the border.

“They are shelling right here, nearly every day now," said a Thai officer. "Very frankly speaking, I really hate these Burmese soldiers."

Once again, a humanitarian catastrophe is looming in this troubled region of South-East Asia.

The Karen insurgency is the longest running in the world. It started in 1949. More than 120,000 refugees live in camps. Some of the camps have been open for more than 20 years.

This new military offensive looks like a final assault, an attempt, perhaps, to neutralise all forms of resistance in the country.