CARACAS - Venezuela's opposition will on Thursday seek to maintain pressure on isolated President Nicolas Maduro after congress chief Juan Guaido swore himself in as interim head of state with the support of nations around the region.Guaido won diplomatic backing from the United States, Canada and right-leaning Latin American governments on Wednesday after declaring himself leader before ebullient supporters who thronged the streets of Caracas in hopes of change. The European Union said the democratic will of Venezuelans "cannot be ignored" and called for the "civil rights, freedom and safety" of Guaido to be respected, but stopped short of recognizing him as leader.The 35-year-old industrial engineer, catapulted almost overnight to national leader, has promised free and fair elections, a transition government to revive the hyperinflation-riddled economy and an amnesty for military officers if they help push Maduro from power.He faces the daunting task of pushing forward the transition plan without control over crucial state institutions and armed forces that have disavowed him.Military commanders, including Defense Minister Vladimir Padrino, have so far promised to stick with socialist Maduro.Russia, which has invested heavily in Venezuela's oil industry and provided support to its armed forces, warned Washington against military intervention and said it would protect the country's sovereignty.Deputy Foreign Minister Sergei Ryabkov told Russian journal International Affairs that Moscow would defend the principle of non-interference in Venezuela's affairs. He did not mention Maduro by name, but made clear Moscow backed his government.Turkey took a similar line, with President Tayyip Erdogan calling Maduro to offer support.Among investors holding defaulted debt issued by the government and state-run oil company PDVSA, the political developments fueled hopes that a resolution of the crisis might be coming closer.Sovereign dollar and PDVSA bonds extended gains early on Thursday, having surged the previous day after Washington backed Guaido.'THE RIGHT TO CHOOSE'Many opposition sympathizers are concerned Guaido could be arrested like other political activists, including his mentor Leopoldo Lopez, who remains under house arrest for his involvement in street protests in 2014."While it's true that Guaido has been recognized internationally, the real power of the state is still in the hands of Nicolas Maduro," said Ronal Rodriguez, a political science professor who focuses on Venezuela at Rosario University in Bogota.With the country's economy falling apart and annual inflation approaching 2 million percent, Maduro has relied extensively on the military to maintain power.Foreign backing could allow Guaido to raise funds abroad to obtain food and medicine for a population struggling under economic crisis, Rodriguez said, but he would face challenges in getting goods through ports controlled by Maduro allies.Guaido on Wednesday promised that humanitarian aid would be distributed with the oversight of congress.He did not announce activities for the coming days.Referring to Wednesday's anti-government protests, the EU said Venezuela's people had "massively called for democracy and the possibility to freely determine their own destiny. These voices cannot be ignored."The Venezuelan people have the right to peacefully demonstrate, to freely choose its leaders and decide its future," the 28-nation bloc said in a statement.The EU has imposed sanctions on Venezuela and boycotted Maduro's swearing-in for a second term this month following a widely-boycotted election last year that many foreign governments called a sham.It aims to set up an international contact group with South American nations in February to seek talks between Maduro and the opposition, which diplomats said would need to include Guaido.European Council President Donald Tusk, who coordinates EU governments from Brussels, took to Twitter to call on "all of Europe to unite in support of democratic forces" in Venezuela.