The charges of US spying are the latest test of relations between the United States and Chavez, a fierce critic of Washington who wants to bring socialist revolution to the world's fifth-largest oil exporter.

Chavez, a close ally of communist-run Cuba, calls George Bush, the US President, "Mr. Danger" and has often charged Washington with planning to overthrow him since he survived a 2002 coup he says was backed by the US government.

"We have uncovered a case, another espionage case," Chavez told an audience at a World Social Forum event on Friday where he was joined by peace activists and Ricardo Alarcon, the National Assembly Speaker of Cuba.

"I warn the US government ... the next time we detect an officer or a civilian official, above all US military officers, trying to get information from our armed forces, we're going to lock them up," he said.

'Confidential evidence'

Venezuelan authorities said on Friday authorities had "confidential evidence" that US Embassy staff were involved with a group of Venezuelan military officers accused of passing state secrets to the US Defence Department.

Earlier this week, Jose Vicente Rangel, the Vice President, said several low-ranking officers had been discovered handing secrets to the United States.

A top army commander on Thursday said the US Embassy was linked to the case.

A US Embassy spokesman said on Friday, "We still have received no official contact from the Venezuelan government on that matter. We are in the dark as to what the details of the charges are."

Populist rhetoric

US officials say Chavez's allegations of plots are populist rhetoric meant to shore up his support among poor voters.

His critics at home and in Washington portray him as an increasing threat to democracy in Venezuela and overseas.

Alonso Medina, an attorney for one man detained in the investigation, said his client, Jacinto Nouel, was a retired firefighter and dentist held on charges of spying and threatening the security of the military.

The lawyer said the prosecutors accused Nouel of ties to the US Embassy after he received documents from his son-in-law, a retired Venezuela naval officer, living in Miami.

Medina said the documents were a CD-ROM with public information about Spanish aircraft.

Veto

Chavez's opponents see him as a threat to democracy

Venezuela clashed recently with the United States over its purchase of Spanish transport and maritime surveillance aircraft as it modernises its armed forces through agreements with Russia, Brazil and Spain.

US officials blocked the sale of the Spanish aircraft.

Washington can veto transfer of US parts to third parties and says it is worried Venezuela's military build-up may destabilise the region.

It did not elaborate on how transport and maritime surveillance aircraft might affect regional stability.