Spanish police arrested a former Venezuelan deputy minister and three former government and state company officials on suspicion of involvement in a massive alleged bribery plot at the country’s state oil company PDVSA, Spain’s Civil Guard said Friday, according to Reuters.

Rafael Ramirez (Photo: Hugoelvictor, CC BY-SA 4.0)The arrests, conducted in concert with the United States Department of Homeland Security, netted Nervis Villalobos, a former deputy energy minister, The Washington Post reported. Also arrested were Rafael Reiter, a former aide to Venezuela’s ambassador to the United Nations, Cesar David Rincon, a former executive at the procurement unit of PDVSA, and Luis Carlos de Leon, the former official at another state-run electric company in Venezuela’s capital, Caracas.

The arrests come as U.S. authorities probe alleged corruption at PDVSA. In 2015, two Venezuelan businessmen, Roberto Rincon and Abraham Shiera, were arrested and indicted in the U.S. for allegedly bribing PDVSA executives.

The U.S. Treasury the same year accused Andorran bank Banca Privada d'Andorra of laundering around $2 billion allegedly embezzled from PDVSA. So far, 10 people have pleaded guilty to paying bribes to Venezuelan officials.

Villalobos was a longtime subordinate of Rafael Ramirez, who was president of PDVSA from 2004 to 2014 and is the current Venezuelan ambassador to the UN. Ramirez has not been charged.

Ramirez denounced the investigation as a U.S. effort to undermine the socialist government of President Nicolas Maduro.