An explosion injured a group of police officers during a protest in Caracas as Venezuelans trickled to the polls to elect a constitutional super-body that unpopular leftist President Nicolas Maduro vowed would begin a "new era of combat" in the crisis-stricken nation.Maduro, widely disliked for overseeing an economic collapse during four years in office, has pressed ahead with the vote to create the all-powerful assembly despite the threat of further U.S. sanctions and months of opposition protests in which more than 115 people have been killed. Opposition parties are boycotting what they call a rigged election.Authorities confirmed three deaths over the weekend, including the killing of a candidate to the assembly during a robbery. Opposition lawmakers said the toll was much higher.