The United States said on Tuesday it has certified the authority of Venezuelan opposition leader Juan Guaido to control certain assets held by the Federal Reserve Bank of New York or any other U.S.-insured banks, a day after it imposed sanctions on the South American country's vital oil industry.

Venezuela has responded strongly by refusing to load crude cargoes without payment and threatening to retaliate. 

The certification, given on Friday, applies to certain property held in accounts belonging to the Venezuelan government or its central bank, according to the U.S. State Department.

On Monday, U.S. National Security Advisor John Bolton announced the sanctions against Venezuela's state-owned oil company Petroleos de Venezuela (also known as PDVSA). He said the sanctions on the PDVSA will block seven billion U.S. dollars in assets and could result in 11 billion dollars in lost sales over the next year. Reuters says the Trump administration appears to be aiming at pressuring President Nicolas Maduro to step down and allowing opposition leader Guaido to call elections. 

In a televised speech on Monday night, Maduro said he would take legal action to challenge the sanctions and defend Citgo Petroleum Corp, PDVSA's U.S. refining subsidiary, which he accused the United States of trying to steal. He also pledged to retaliate, but did not announce any specific measures.

"We will provide the reciprocal and convincing response needed to defend Venezuela's interests in due time," Maduro said.

Venezuela's envoy on Tuesday accused the U.S. of preparing a "military invasion" at an UN-sponsored Conference on Disarmament. The country's ambassador Jorge Valero said that the Trump administration was preparing a "military invasion" of his country and questioned whether Washington had the moral authority to "impose a diktat" on Caracas.  

Bolton did not rule out of the use of military acts during the news briefing on Monday. He warned Maduro that he would be held responsible for the safety of U.S. diplomatic personnel in Venezuela as well as Guaido and other opposition figures.

He also did not appear to rule out U.S. military intervention, though such action is widely considered to be unlikely.

Maduro says the United States is promoting a coup against him and promised to stay in office. On Sunday, the president, alongside Defense Minister Vladimir Padrino, oversaw a military parade to show military force and loyalty.

The socialist leader said the display showed the world he had the backing of the military, and that Venezuela's armed forces were ready to defend the country.

Shortly after the U.S. sanctions, three sources told Reuters that PDVSA has ordered customers with tankers waiting to load Venezuelan crude bound for the United States to pay for the cargoes before they depart.

Venezuela exports about 500,000 barrels per day of crude to the United States. Citgo, Valero Energy Corp and Chevron Corp are the three largest buyers of Venezuelan crude in the U.S.

Traders and shippers with tankers anchored around Venezuelan ports said they saw no clear way for U.S. customers to pay for Venezuelan crude after sanctions, even if payments are intended to be made before loading.

According to the new sanctions, any proceeds from Venezuelan crude exported to U.S. companies will stay in special bank accounts in the United States. 

(Top image: Venezuela's President Nicolas Maduro gestures following a televised press conference in Caracas, Venezuela, January 25, 2019. /VCG Photo)