Venezuela on Tuesday arrested the acting president and five other top executives in charge of Citgo, the US refinery subsidiary of troubled state oil company PDVSA, on corruption charges.

"Six senior executives have been arrested," said chief prosecutor Tarek William Saab, adding that the charges included embezzlement, bid rigging, money laundering and criminal association. 

He speculated that they might have been assisting "a foreign power" pursuing an anti-Venezuelan strategy -- an allusion to the United States.

The Citgo chief, Jose Angel Pereira, was arrested in Caracas.

The place and circumstances of the arrests of the other executives -- Citgo vice presidents Tomeo Badel, Alirio Zambrano, Jorge Toledo, Gustavo Cardenas and Jose Luis Zambrano -- were not given.

Their arrests come just a week after Saab announced the detention of a deputy minister and nine PDVSA officials for allegedly doctoring crude oil production figures. 

A Citgo official said the company was "looking into the current investigation" in Venezuela.

In all, around 50 PDVSA employees have been arrested under an anti-corruption drive led by Saab since he took office as the country's attorney general in August.

- Sensitive asset -

Venezuela: the decline of energy giant PDVSA 
Venezuelan President Nicolas Maduro backed the detentions and called for PDVSA workers to give their support "in this hard and difficult struggle" against corruption suspects.

"I will go all the way and nothing and nobody will stop me" in seeing through the anti-graft campaign, he said. 

The rash of arrests underline the debt woes swirling around PDVSA, which is the prime source of income for Venezuela, a country that sits atop the world's biggest oil reserves.

Both PDVSA and Venezuela are staring down the barrel of default on a debt pile estimated at up to $150 billion, around a third of which is paper issued by the oil company.

A partial default has already been declared by major credit ratings agencies, and an influential creditors' committee has ruled that PDVSA failed to make payments on time. 

That is setting the scene for all holders of Venezuela government and PDVSA debt to possibly call in their IOUs at once -- an impossible situation for Caracas, which has less than $10 billion in hard currency reserves left.

Maduro has said he wants to refinance and restructure Venezuela's debt, whose hefty servicing is diverting needed funds from imports of food and medicine, both of which are severely lacking in his country.

But that effort is complicated by sanctions from Washington that ban US entities from buying new, long-term debt from PDVSA or the Venezuelan government, or from dealing with certain key Venezuelan officials.

Citgo is an especially sensitive asset for PDVSA, which bought full control of it 27 years ago -- before the socialist regime installed in Venezuela by President Nicolas Maduro's late predecessor, Hugo Chavez, came to power in 1999.

- Debt collateral -

The subsidiary has three oil refineries in the United States, in the states of Texas, Louisiana and Illinois. They have a total refining capacity of 750,000 barrels per day, or around four percent of total US refining production. The three plants employ about 4,000 people. 

Citgo also owns three pipelines and stakes in three more. It has 48 petroleum terminals.

Venezuelan Attorney General Tarek William Saab said the arrest of the six senior Citgo executives was related to contracts they signed with Frontier Group Management and Apollo Global Management for a supposed restructuring of $4 billion in debt 
But PDVSA has put 50.1 percent of Citgo up as collateral to guarantee its debts, particularly to Russian state oil giant Rosneft. That has unnerved US authorities who don't want to see the company fall into Russian hands.

Saab said the arrest of the six senior executives was related to contracts they signed with two companies, Frontier Group Management and Apollo Global Management, for a supposed restructuring of $4 billion in debt.

He said the terms of the restructuring were "unfavorable for our main industry, which is PDVSA," and "most seriously" offered Citgo as a debt guarantee. 

Saab drew on information from WikiLeaks and the Panama Papers as evidence against Pereira and others.

"This is the most rotten sort of corruption that needs to be punished and sanctioned, independent of who is involved, even the highest management of Citgo. They have to answer to justice," Saab said