Anglo-French oil company Perenco and Russian financial firm Gazprombank have been identified in testimony by a former Venezuelan state oil company official who said he received millions of dollars in bribes in return for giving them preferential treatment, a source with knowledge of the matter said on Thursday.

Abraham Ortega, a former financial executive at state oil company PDVSA, accepted $5 million in bribes to favour a French oil company and from a Russian bank, US prosecutors in Florida said on Wednesday in a statement, which did not name either company. Ortega received $3 million to help the French company and $2 million to favour the Russian one, according to the Department of Justice announcement.

Prosecutors said that in exchange, Ortega helped the companies gain "priority status" to loan money to oil joint ventures in which they were partners with PDVSA.

The high-profile case is one of a slew of US probes into corruption in Venezuela, which is reeling from hyperinflation, empty shelves and mass emigration, but the case is one of the first to link corruption in the oil sector to prominent foreign firms.

Perenco declined to comment. Gazprombank and PDVSA did not immediately respond to requests for comment.

The case stemmed from cash-strapped PDVSA's chronic delays in paying dividends to foreign firms, a second source said.

Perenco was desperate to receive those funds and get the money out of Venezuela, according to the source. Perenco agreed to loan money to the Petrowarao joint venture it ran with PDVSA, but as part of the deal had to be paid its late dividend payments beforehand.

The company received those payments in late 2013, the source said. Former oil minister Rafael Ramirez, who is now on the run from leftist President Nicolas Maduro's government, announced in 2014 that Perenco was loaning $420 million to Petrowarao to quintuple its oil production to 24,000 barrels per day.

However, the source said that Perenco ended up loaning a small fraction of the promised amount.

In total, Ortega said he accepted $17 million in bribes as part of a broad embezzlement scheme. The money was hidden in the United States, Switzerland and the Bahamas, according to the U.S. prosecutors.