"We urge President Maduro to reconsider the decision to bar Capriles and ensure Venezuelans can exercise their right to elect their representatives in free and fair elections", the US State Department said in a statement.
Venezuela is now in the state of economic emergency, announced by country's president in January 2016 amid widespread food shortages, hyperinflation and anti-government protests. The freedom of assembly is a universal human right which the Venezuelan authorities must respect.
Daniel Queliz was shot in the neck as police broke up protesters who want to remove Maduro from office over a spiraling economic and political crisis.
Most of the protesters are peaceful and say street action is their only option after authorities previous year blocked a recall referendum to remove Maduro.
Nine people, including two teenagers, were arrested for breaking into an office of the Supreme Court and vandalising it at the end of Saturday's march.
Some 188 protesters, a lot of them students, were arrested in the period April 4-8 and 57 are still behind bars, rights group Penal Forum said on Monday.
Opposition groups also called on their supporters to organise protests in other Venezuelan cities under the banner "no more dictatorship".
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Venezuela's opposition activists clash with riot police agents during a protest against Nicolas Maduro's government in Caracas on April 4, 2017.
The court aimed to assume the functions of the opposition-led Congress, sparking outcry among Venezuelans already suffering from triple-digit inflation and widespread shortages of basic goods.
An 87-year-old woman was reported to have died in her apartment in the Colinas de Bello Monte neighbourhood after inhaling tear gas thrown by police during street demonstrations.
The almost-daily churn of events in what the opposition calls an "ongoing coup" by the government has energized and united the normally fractious opposition.
Mr Capriles has been at the forefront of demands for a recall referendum on President Maduro and was seen as the opposition's best hope in next year's presidential election.
The protest movement's immediate goal apparently is to force Maduro to call elections.
"The national guard is pummeling thousands of peaceful protestors", Duarte said.
As the sea of protesters approached the headquarters of state-run PDVSA oil company, they were met by rubber bullets and a curtain of eye-scorching tear gas, some of it a never-before-seen red color.
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