Caracas - As Venezuela's economic crisis deepens, President Nicolas Maduro has stepped up accusations of plots against his leftist government, lashing out most recently at US Vice President Joe Biden.Just ten days ago, Maduro had fondly referred to Biden as "comrade", but on Sunday the Venezuelan leader was livid.At a rally with several thousand supporters, Maduro angrily accused Biden of going behind his back in talks with regional leaders "to announce the overthrow of my government”.State Department spokesperson Jen Psaki said the allegations were "baseless and false", and an attempt to distract from what's taking place inside the country."The Venezuelan government should focus on the legitimate grievances of its people, which include repeated violations of the freedom of speech and assembly, as well as due process under the law," she said.Psaki also announced that the United States has imposed visa restrictions on more current and former Venezuelan officials who it deems to have engaged in human rights abuses and "acts of public corruption". The officials were not identified.‘Vulgar’Maduro on Monday responded calling the new sanctions as "vulgar" and "offensive".Maduro's popularity has plummeted to 20% over the past year, as the oil-rich country's many woes - dire shortages, a shrinking economy, and high crime - have grown worse.Signs that the government feels under siege have become more pronounced with the plunge in the price of oil, the mainstay of the Venezuelan economy.Maduro spent 19 days out of the country in January, seeking to shore up oil prices and attract investments in visits to the Middle East, Russia and China, with little to show for his efforts.His brief stays in Venezuela, meanwhile, have been punctuated by angry denunciations of plans for "a coup d'etat," "psychological warfare," "ambush," "plotting" and "economic war.""Maximum alert!" Maduro warned his followers on Sunday. "A plan for a bloody coup d'etat has been put into motion and we must unite popular forces and the military to defeat any coup scenario."Comrade BidenThe attacks against the US vice president began on Friday, four days after Biden wooed Caribbean leaders who rely on Venezuela for subsidised oil supplies at a conference on energy security.As Maduro prepared to leave Caracas for a meeting with Latin American leaders in Costa Rica, he charged that a "terrorist group" had gone to the Central American country to "try to threaten me”.On his return on Friday, he went on television to say that at the meeting various unidentified presidents had warned him that the United States was plotting against him, and "to watch out for Biden”."In Washington, they met with all the governments of the Caribbean and told them that the government of Venezuela was going to be overthrown.""Vice President Biden, look me in the eyes: Is this what you want for relations with Latin America and the Caribbean?"The week before Maduro lashed out against a visit by ex-presidents of Colombia, Mexico and Chile who were blocked from visiting jailed opposition leader Leopoldo Lopez.Maduro said the three - Felipe Calderon of Mexico, Sebastian Pinera of Chile, and Andres Pastrana - were coming "to support an extreme right group that is calling for a bloody coup d'etat”."If a coup d'etat were to occur you would be stained with blood," he said.