By Paulo Prada

RIO DE JANEIRO (Reuters) - Venezuela and indigenous groups are disputing whether an alleged massacre of Amazon villagers took place after Venezuela's government said it found no evidence of an attack.

A group representing the Yanomami tribe last week said that Brazilian gold miners had crossed the border and attacked a village from a helicopter. It said the assault could have killed more than 70 people.

Though the attack allegedly happened in July, the tribe was only able to alert the government recently because of the distance and isolation of their native region along the long, dense jungle border with Brazil.

Venezuelan officials said over the weekend that flyovers of the area led them to believe that the allegations were false.

"We can tell the country that we have seen no evidence of death," said Nicia Maldonado, Venezuela's minister of government affairs, in televised comments.

Native rights groups and some local politicians criticized the government, saying it reached that conclusion prematurely.

The remoteness of the region - and the nomadic habits of the Yanomami tribe - make it unlikely officials could have reached the exact spot where the attack was reported to have taken place, they said. Even natives, they point out, take days to move among settlements in the region.

In a collective statement, 11 tribes and rights groups including the Yanomami said, "It cannot be said that there isn't evidence" and pressed the government to continue investigating.

Liborio Guarulla, an indigenous Venezuelan and governor of Amazonas, the southern state where the attack is said to have happened, accused the government of "mobilizing resources just to silence the matter."

To some officials, the allegations of an assault by foreign aggressors, wielding guns and explosives from a helicopter, is difficult to believe. Not only would assailants need resources, know-how and familiarity with terrain not easily accessed from above, they would need knowledge of the habits and whereabouts of the Yanomami, who live in small groups and change settlements frequently.

"It would be extremely hard to do," said General Rafael Zambrano, commander of the Venezuelan army unit responsible for the region. Zambrano in a telephone interview said a small patrol of troops continues to inspect the area just in case.

YANOMAMI REQUEST UNUSUAL

People familiar with the Yanomami said their request for an investigation is unusual because tribal tradition frowns on discussions of the dead.

"It's a measure of how serious the problem is that they are making these allegations," said Marcos Wesley de Oliveira, coordinator of a regional program for indigenous people at the Instituto Socioambiental, a Brazilian advocacy group.

The tribe's native land on both sides of the border in recent decades has come under increasing pressure from wildcat gold miners and other outsiders.

Brazil's government last week said it asked Venezuela for more information about the alleged attack and whether Brazilians were involved. On Monday, Brazil's foreign ministry said it hasn't yet received any request from Venezuela for help investigating.

If an attack occurred, it remains unclear how many victims there may have been.

In the document they presented to Venezuelan authorities, the tribe said that only three members of the village are known to still be alive.

Those three, the document said, had been hunting when they heard the sound of a helicopter, gunfire, and explosions. The hunters, the document said, alerted Yanomami from another settlement, who went to the village and found charred bodies.

(Additional reporting by Peter Murphy; Editing by Cynthia Osterman)