At least two protesters were killed on Wednesday in Venezuela as clashes broke out on the sidelines of a mass anti-government rally that the opposition billed "the mother of all marches".
Recent moves by Maduro to tighten his grip on power and ban Capriles from politics have escalated the country's political and economic crisis and sparked worldwide cries of concern.
Speaking to reporters Wednesday, Secretary of State Rex Tillerson said the U.S. is "concerned that the government of Maduro is violating its own constitution and is not allowing the opposition to ... organize in a way that expresses the views of the Venezuelan people".
Government supporters held opposing demonstration as backers dressed in red t-shirts and carried posters of popular late President Hugo Chavez, who governed from 1999 to 2013.
Demonstrators clash with riot police during the "mother of all protests" in Caracas, Venezuela, on April 19.
A Venezuelan teenager who was shot in the head near anti-government protests in the capital has died.
Lawmaker Olivia Lozano told the El Nacional newspaper the perpetrators were supporters of the ruling party.
The seizure came as tens of thousands of protesters demanded elections and denounced what they consider to be an increasingly dictatorial government.
Seven protesters have been killed in demonstrations against Maduro's government, the BBC reported.
A 17-year-old boy died after being shot by an unidentified man on a motorcycle in the head, witnesses said.
Maduro's opposition is also demanding new elections, which were indefinitely postponed past year - mere months after Maduro also canceled a recall referendum that could have ousted him from power.
After today's march, the risk of violence will continue as the government is determined to maintain its power and close the electoral path, said Maria Teresa Urreiztieta, a social psychologist at Simon Bolivar University in Caracas.
There have been five other deaths nationwide tied to protests that began in early April after the Supreme Court gutted the opposition-controlled congress of its last remaining powers.
In that reference, president Maduro added that together "with the political work" by the Government, the people should also remain alert in order to respond to the unpatriotic strategies and actions by the right and the interference encouraged from the Organization of American States.
US President Donald Trump has not said much publicly about the crisis in Venezuela. He said he was "anxious" to see elections take place sometime "soon" and repeated his call for dialogue, saying he had a proposal he wanted to make the opposition. After the CNE quashed an effort to hold a recall referendum on Maduro's presidency in the fall of 2016, it's not beyond the realm of possibility that these elections might be postponed indefinitely or at least until a sufficient number of opposition parties fail to meet the requirements for renewal.
The opposition attributed both deaths to groups known as "colectivos", armed government supporters who are frequently accused of involvement in confrontations during protests.
With its momentum renewed, the opposition is now pushing for Maduro's removal and the release of scores of political prisoners.
The public prosecutor's office has called for an investigation into the shooting.
He also told them they needed to use all their political weaponry to combat the lies of Mr Maduro's "fascist" opponents. "We again urge demonstrators to express themselves non-violently", Toner said.
Maduro on Tuesday activated the "Zamora Plan" - a military, police and civilian operation aimed at combatting a supposed coup attempt - which the president says is being orchestrated by Venezuela's opposition and the United States. He also said authorities in recent hours had rounded up unnamed members of an underground cell of conspirators at Caracas hotels, including some who were allegedly planning to stir up violence at the march.