KALANDAO, Central African Republic – The rumble of engines is the signal for the villagers here to flee, leaving behind smoldering pots of wild roots and leaves, a meager afternoon meal.

The Central African Republic – important as a potential bulwark against the chaos and misery of its neighbors in Chad and the Darfur region of Sudan – is being dragged into the conflict that has begun to engulf central Africa.

So porous are its borders and ungoverned are parts of its territory that foreign rebels are using the Central African Republic as a staging ground to mount attacks over the border, spreading what the United Nations has already called the world's "gravest humanitarian crisis."

The situation is so bad in some places that 50,000 residents have fled the CAR to find refuge in Chad, of all places, while starvation threatens hundreds of thousands who remain.

"This is the soft belly of Africa," said Jerome Chevallier, a World Bank official who is trying to help stabilize the CAR. "It has little protection from whatever might strike it."

The Kalandao residents had fled their country's own army, which has been burning villages to smoke out a homegrown rebel movement bent on overthrowing the government. Once the villagers realized the approaching vehicles were from the U.N. World Food Program, they trickled back to tell their story.

"We are living in the bush like animals," Leontine Makanzi said. "Our children are dying. We are eating nothing."

The Central African Republic is one of the poorest countries in the world. In few places do people live so short a lifespan, bury so many of their young children or succumb more to treatable disease.

Its vulnerability has grown in recent months. On its border with Sudan, Chadian rebels supported by the Sudanese government have built a base, according to government officials and diplomats, to bolster their bid to overthrow Chad's president, Idriss Deby.

Now the CAR government says these foreign fighters have teamed up with local rebels to overthrow it as well, making it increasingly hard to separate one conflict in the region from another.

"The world must act now to prevent an even graver crisis here," said Jean-Charles Dei of the U.N. World Food Program. "The international community must act to protect these vulnerable people or risk that they will be consumed by the crisis in the region."