CARACAS, Venezuela (Reuters) -- Venezuela said on Friday authorities had concrete evidence that U.S. Embassy staff were involved with a group of Venezuelan military officers accused of passing state secrets to the Pentagon.

The charges of U.S. espionage are the latest test to relations between the United States and Venezuelan President Hugo Chavez, a fierce critic of Washington who says he is bringing socialist revolution to the world's No. 5 oil exporter.

"The Venezuelan state has confidential information, thoroughly confirmed, that officials from the U.S. military mission are involved in this," Vice-President Jose Vicente Rangel told reporters.

U.S. Embassy representatives have said the Venezuelan government has not contacted them on the espionage charges.

"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," a U.S. Embassy spokesman said.

Chavez, whose closest ally is Cuban President Fidel Castro, has often charged Washington with plotting to kill him or undermining his government. He survived a brief 2002 coup he says was backed by the U.S. administration.

U.S. officials say Chavez's allegations 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.

Earlier this week, Rangel said several low-ranking officers had been discovered handing over state secrets to the U.S. Defense Department.

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

Officials have not said how many officers were involved or confirmed that anyone has been detained.

Military authorities have said an investigation was underway, but a navy spokesman said he could not comment on the probe.

Rangel said the Foreign Ministry would be responsible for contacting U.S. officials.

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 U.S. 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.

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

U.S. officials blocked the sale of the Spanish aircraft, which contained U.S.-made technology. Washington can veto transfer of U.S. parts to third parties. U.S. officials say Venezuela's military buildup may destabilize the region.