Venezuela's President Nicolas Maduro said authorities had captured a US spy targeting a pair of refineries on the north Caribbean coast as the country once wealthy from oil is gripped by a severe shortage of fuel. Mr Maduro alleged the spy was a Marine who had served as a CIA operative in Iraq. He gave no identity or other immediate proof to support the claim, saying more details would follow, such as photos and video. The suspect was captured on Thursday while possessing specialised weapons and a large sum of dollars, Mr Maduro said on Friday, adding that the man was being interrogated about his activities around the Amuay and Cardon refineries in Falcon state. Mr Maduro, an adversary of the United States, also said Venezuelan authorities had dismantled a plot on Wednesday that was aimed at blowing up a third refinery, El Palito in Carabobo state. He urged the nation's oil workers to be on alert for more attacks. “The gringo empire wants revenge against Venezuela,” he said. “It wants to prevent Venezuela from producing all petroleum products, gasoline.” Oil once made Venezuela a wealthy nation, but critics of Mr Maduro say two decades of socialist rule have left it near ruin. Its dilapidated oil fields and refineries barely produce, and the nation today relies on imports from Iran, another US foe. A second, severe scarcity of petrol struck in recent days, forcing motorists to queue for hours and days to fill their tanks, even in the capital of Caracas. Analysts say the next three Iranian ships bringing fuel will not arrive for weeks. The United States recently seized a second shipment of fuel sent by Iran. While Venezuela's broken oil industry leaves drivers stranded, stiff US sanctions have also blocked Mr Maduro from importing gasoline. If Mr Maduro's claim of arresting a US citizen are correct, the suspect would join two former US special forces soldiers already jailed in Venezuela for allegedly participating in a failed attempt to overthrow the socialist leader. The two men were arrested in early May among more than 80 rebel Venezuelan fighters who staged a failed beach attack called Operation Gideon that was aimed at seizing Mr Maduro. The soldiers – identified as Luke Denman Airan Berry Venezuela – have been sentenced to 20 years in prison. Venezuelan authorities say they confessed to being part of the plot. While the Trump administration denied having anything to do with the blundered May incursion, Washington backs Venezuelan opposition politician Juan Guaido who seeks to overthrow Mr Maduro.