(Adds details on investigation, context on Ramirez)
CARACAS, Dec 12 (Reuters) - Venezuela will open a criminal investigation of former oil czar Rafael Ramirez, the country's chief prosecutor said on Tuesday, as part of a broad shakeup of the OPEC nation's oil industry that has resulted in the arrest of dozens of executives.
Ramirez, who until this month served as Venezuela's representative at the United Nations, denies being involved in corruption and has criticized President Nicolas Maduro for the steady decay of the country's oil industry.
Ramirez left New York this month, and his current whereabouts are not public. He did not immediately respond to a request for comment on Tuesday.
Maduro in recent weeks has named new leadership to the country's ailing state oil company PDVSA and praised what he calls an anti-corruption campaign in which some 67 oil industry managers have been arrested.
Opposition critics say the recent spate of arrests is motivated by internal divisions in the ruling Socialist Party, and insist that Maduro has turned a blind eye to corruption when it was politically expedient to do so.
"We have decided to open a criminal investigation ... of Rafael Ramirez, ex Oil Minister and (ex) President of PDVSA," said Prosecutor Tarek Saab in a televised address.
He said the decision resulted from a review of documents known as the Panama Papers that showed Ramirez had been involved in the "intermediation" of oil sales together with his cousin Diego Salazar, who was arrested this month.
Between 2004 and 2014 Ramirez was the most visible face of late socialist leader Hugo Chavez's oil sector nationalizations that boosted state control over the industry.
After clashing with Maduro, he was named foreign minister and then U.N. diplomat.
But he was forced from his U.N. post last month, in part because of a series of articles criticizing the management of PDVSA, which has seen its production drop to the lowest level in decades amid a broader economic crisis.
Last month the authorities arrested Eulogio Del Pino and Nelson Martinez, both of whom served as oil minister and PDVSA president, on corruption charges. (Additional reporting by Andreina Aponte, writing by Brian Ellsworth; Editing by Alexandra Ulmer and Susan Thomas)