The Guarani-Kaiowa Indians of central Brazil are desperately urging authorities to demarcate their ancestral lands to stop plans to evict them in a dispute with wealthy white ranchers, a Catholic Church group said Thursday.

"Last week, several disputes flared between Indians and ranchers in Mato Grosso do Sul due to slow government efforts to demarcate indigenous lands," Rui Posati, a spokesman for the Church-linked Missionary Council for Indigenous Peoples (CIMI), told AFP.

Guarani Indians, whose total population in Brazil is estimated at 46,000, have been trying to recover a small portion of their original territories, but face violent resistance from wealthy ranchers as well as soya and sugar cane plantation owners.

In a letter sent to CIMI, judicial authorities and the Brazilian presidency, the Guarani-Kaiowas said a recent ruling by state judicial authorities on the land disputes forced them to abandon an area near several ranches in Iguatemi, a town located 500 kilometers (300 miles) from the state capital Campo Grande.

This amounts to decreeing "their collective death," said the group of 170 natives.

"This ruling is part of the history of extermination of Brazilian Indians. We have lost any hope of surviving in dignity, without violence, on our ancestral lands. We will all die soon," their letter said.

The violence is linked to land disputes in a country where one percent of the population controls 46 percent of the cultivated land.

On Thursday, Survival International, a leading advocate for tribal peoples' rights, charged that the 170 Guaranis have little food and medical care and that their territory is currently being occupied by hostile ranchers.

The National Indian Foundation (FUNAI), tasked with demarcating Guarani lands, meanwhile said it was trying to get the eviction order rescinded.

But a Survival statement said the slow process meant that thousands of Guaranis are forced to live on crowded reservations or in makeshift roadside camps.

"They face one of the highest suicide rates in the world," Survival said, urging that the Guaranis be allowed to live on their lands and that all their territories be demarcated "before other lives are lost".