Protesters in the capital and other cities marched on military installations, where they demanded an end to "brutal repression" and called for Maduro's resignation and new elections.
"Let's send a message to the armed forces: Are you going to continue killing Venezuelans or respect the Constitution?" opposition deputy Jose Manuel Olivares said.
A 22-year-old protester died outside the base on Thursday, three days after a 17-year-old was killed when national guardsmen opened fire. The death toll in three months of protests now stands at 75.
The government and opposition blame each other for the violence. The opposition coalition known as MUD called on the military on Saturday to "lower its weapons."
Saturday's protests coincided with the commemoration of the Battle of Carabobo of June 24, 1821, which marked a decisive step towards Venezuela's independence from colonial rule.
Addressing a crowd after a traditional military parade, Maduro claimed that an unspecified number of people had been detained and would face military trial over an alleged coup plot, backed by Venezuelan opposition leaders and aimed at precipitating a US intervention in the country.
Maduro has repeatedly claimed that the United States is to blame for the grave political and economic crisis in the oil-producing country, which has fueled the often violent demonstrations of recent months.
"All the detainees are under military jurisdiction because they are involved in the coup, and have violated laws fundamental to the independence, peace and sovereignty of our country," he said. "They will be severely judged."
"I am not exaggerating when I say it would have involved the arrival of American ships and troops in Venezuelan waters, on Venezuelan soil," Maduro said.
War of words
Earlier Saturday, the head of the Organization of American States dug in his heels in a war of words with Caracas, flatly rejecting its demand that he resign in exchange for the country's continued membership in the regional body.
Luis Almagro, the OAS secretary-general, has been at the center of an angry tiff between the organization and the Maduro government, which in April initiated the two-year process of withdrawing from the group.
Brushing off Maduro's suggestion that he step aside, Almagro said in a video, "We will never give up until we have the freedom of Venezuela in our hands."
He said he would resign only "when free and transparent national elections are held ... (and) when all political prisoners are released and exiles are given amnesty."
He set a further condition: the prosecution of "the murderers of each of the protesters, as well as of their chain of command."
Despite Almagro's efforts, the OAS General Assembly, meeting this week in the Mexican resort of Cancun, was unable to reach agreement on a plan to deal with the instability in Venezuela.
Maduro called the OAS's failure to advance a plan "a diplomatic and political victory" for Venezuela, and said his country would "never" return to the grouping.
Meantime, Maduro's critics were angered anew on Saturday after the release of a video on which an opposition leader's voice is allegedly heard crying out from a prison window that he is being tortured.
"Lilian, they are torturing me! Report them! Report them!" the voice of Leopoldo Lopez is said to be heard on a video made by his wife, Lilian Tintori, outside the Ramo Verde military prison near Caracas.
Tintori said her husband, a leader of the Popular Will party, is being held incommunicado.
Lopez is serving a sentence of nearly 14 years after being convicted of inciting violence during anti-Maduro protests in 2014 that left 43 people dead. Human rights groups have called the charges politically motivated.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)
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