Venezuela’s government has frequently alleged coup plots, often without providing much evidence or follow-up.A study by the Caracas-based newspaper Ultimas Noticias counted 63 alleged assassination plots between when late President Hugo Chavez took office in 1999 and his death in 2013.President Nicolas Maduro’s government has denounced more than a dozen purported plots since coming to power 15 months ago.Last spring, Maduro announced that three air force generals had been arrested after they were discovered plotting with opposition politicians to overthrow the government. Officials have said nothing about the case since.The most serious recent allegations came in late May, as authorities tried to mop up dissent that led to a three-month wave of deadly antigovernment protests.Top officials delivered an hours-long presentation in which they accused a handful of opposition leaders of working with the US ambassador in neighboring Colombia to ‘‘annihilate’’ Maduro.Those who believe the government are a quick to recall Washington’s endorsement of a coup that toppled Chavez for two days in 2002.