A top Venezuelan opposition figure called on Saturday for more marches aimed at taking back the courts and the National Electoral Council that he said had been "hijacked" by President Nicolas Maduro. Freddy Guevara urged people to protest on Monday -- May 1 or May Day, a traditional workers' holiday -- with marches to the Supreme Court and the National Electoral Council's offices. "We want to summon all Venezuelans, across the country's 24 states, to hit the dictatorship with a one-two punch," Guevara said, evoking simultaneous peaceful marches in the two locations. A month of demonstrations in April in Venezuela has left 28 people dead in clashes between riot police and anti-government protesters, according to prosecutors. More than 400 people have been injured, and nearly 1,300 arrested, according to the attorney general. The center-right-led opposition is demanding elections to remove Maduro, an elected socialist. It blames him for an economic crisis that has caused shortages of food, medicine and other basic items. "On May 1, after a month of resistance, we need to show that the people refuse to give up," Guevara said. Late Saturday, hundreds of people marched by candlelight, flowers in their arms, to pay homage to those killed in the latest protests. "We are here to remember our friends who have been killed seeking the release of those on our side who have been jailed. The (dead) deserve this recognition from all of Venezuela," said law student Amanda Fioretti, 20. Rights group Amnesty International urged the government on Wednesday to stop the "persecution" and "arbitrary detention" of protesters. - Pope could mediate - Earlier in the day, Pope Francis said the Vatican was ready to intervene as a mediator to try and end Venezuela's deadly political crisis under "clear conditions." Speaking on a plane bringing him back from Egypt to Rome, the pontiff said: "I believe that must be done under conditions. Very clear conditions." "There was an intervention by the Holy See following strong pressure" by four former leaders of Spain, the Dominican Republic, Panama and Colombia, he said. "This did not work because the proposals were not accepted. They were diluted. It was a 'yes, yes but no, no,'" he said. The pontiff said the four mediators were trying to relaunch the process, adding "they are looking for a venue" but the opposition was against the process. "We should do all that we can for Venezuela with necessary guarantees," he said. The pontiff did not clarify the conditions. But his Secretary of State Pietro Parolin, the former papal nuncio in Venezuela, had in December spoken of four prerequisites: the establishment of an election timetable, the freeing of opposition supporters held in prison, allowing foreign health aid and giving the legislature back its powers. But senior opposition leader Henrique Capriles dismissed the idea of resuming dialogue with the government. The pontiff "speaks as if some wanted dialogue and others did not," Capriles told journalists at a memorial for those who had died in April protests. "We Venezuelans all want dialogue, but we are not disposed to a Zapatero dialogue," he said, referring to Spain's former prime minister Jose Luis Rodriguez Zapatero, who led last year's Vatican-backed mediation bid between the goverment and the opposition. Just Wednesday Venezuela said it was quitting the Organization of American States in anger at pressure from the bloc over the government's handling of its political crisis. Echoed by the United States and European Union, the OAS has led an international chorus of concern over the economic and political chaos in the major oil-exporting country. Venezuela has suffered an economic collapse fueled by a plunge in international prices for its crucial oil exports. Maduro says the shortages and the protests are part of a US-backed plot to topple him.