As new protests flare, a war of words breaks out between Caracas and the head of the Organization of American States.

Thousands of Venezuelans marched on Saturday in a new flare-up of months-long protests against embattled President Nicolas Maduro, as the head of the Organization of American States dug in his heels in a war of words with Caracas, brusquely rejecting its demand that he resign.

Protesters in the Venezuelan 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 in Caracas, as protesters prepared to march on the La Carlota airbase.

David Vallenilla – 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.

Young protesters broke down a metal fence guarding the airbase in Caracas before being repelled by security forces firing tear gas.

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The opposition coalition, known as MUD, called on the military on Saturday to “lower its weapons”. The government and opposition blame each other for the violence.

Al Jazeera’s Teresa Bo, reporting from the anti-government protests in Caracas, said demonstrators had told her they believe a proposed constitutional change by Maduro is an excuse by the government to hold onto power. A vote on the changes is set to take place on July 30.

“People here say that their fight here is gong to get much more intense until that time comes,” she said.

“They are calling for civil disobedience and they’re saying that they will remain on the streets for as long as it takes.”

David Vallenilla, a 22-year-old protester, died outside La Carlota base on Thursday [Christian Veron/Reuters]

War of words: OAS and Caracas

Earlier on Saturday, the head of the Organization of American States (OAS) flatly rejected a suggestion by Maduro 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 centre of an angry tiff between the organisation and the Maduro government, which in April initiated the two-year process of withdrawing from the group.

Venezuela has grown increasingly irritated by Almagro’s pointed criticisms. He has accused the government of violating human rights, interfering in elections and detaining political prisoners.

A grave political and economic crisis in the oil-producing country has driven the often violent demonstrations of recent months.

Brushing aside 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.”

Torture claim

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.

At a press conference with foreign reporters, he said that Almagro should step down and allow OAS member countries to “rebuild and reorganise” the institution – the only way, he said, that “I would think of returning.”

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Meanwhile, 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.