CARACAS, Venezuela -- Venezuelan formally notified the Organization of American States on Friday of its intention to leave the regional body amid sometimes violent protests at home and international calls for its government to hold delayed elections and release prisoners.

Venezuelan interim ambassador Carmen Velasquez submitted a letter announcing the move in Washington to OAS Secretary General Luis Almagro, a fierce critic of embattled President Nicolas Maduro. The notice begins a two-year exit process.

"This is a historic moment that marks a new independence for Venezuela and the region," said Velasquez, adding that Venezuela would be the first country to leave the Washington-based bloc this way. "We are not going to be participating in any OAS activities."

The decision to leave the OAS comes amid almost daily clashes between security forces and anti-government protesters that have left at least 28 people dead and hundreds injured.

On Friday, hundreds marched to a military prison outside Caracas to demand the release of opposition leader Leopoldo Lopez and other jailed activists they consider political prisoners.

The march was part of an intensifying campaign by the opposition to force Maduro from office. More than 1,300 people have been arrested in almost four weeks of street clashes.

Marchers wound through side streets on the way to the prison, shouting "Maduro out!" and waving Venezuelan flags. Light armoured vehicles and national guardsmen blocked access to the Ramo Verde military prison where Lopez is serving a nearly 14-year sentence for inciting violence during a previous round of anti-government unrest in 2014. With access blocked, the march ended 2.5 miles from the prison.

Protesters also marched to prisons in other cities where they say 178 people are being held on political charges.

Many foreign governments and human rights groups condemned Lopez's conviction as politically motivated. One of the prosecutors in the case, who has since sought asylum in the U.S., even said he was under orders from the government to arrest Lopez despite a lack of evidence.

Lopez's wife Lilian Tintori was at the front of a group of lawmakers and opposition activists carrying a large Venezuelan flag making their way to the prison. In a telephone interview with Colombia's Blu Radio, said she hadn't been allowed to see her husband since April 6 because authorities were punishing them for promoting protests. There was no immediate response from the government.

"For Maduro, not being on his side is a crime, thinking differently is a crime," she said. "They forgot what democracy is."

Venezuela's decision to leave the OAS comes after a contentious meeting at the group's headquarters in which its permanent council voted in favour of holding a special session to evaluate Venezuela's crisis, adding to mounting international pressure for Maduro to schedule delayed elections and free detained political activists.

Tension have been steadily rising between Venezuela and a group of OAS members that includes the United States since Almagro issued a 75-page report in March accusing Maduro's government of systematically violating human rights and standards of democracy.

At a news conference at his country's consulate in New York on Friday, Samuel Moncada, Venezuela's deputy minister of foreign affairs for North America, said his country is pulling out of the OAS because the group has become a forum for "coercion" instead of co-operation.

Moncada accused the United States of pressuring other, smaller countries not to stand with Venezuela in the organization, saying the OAS has "degraded into an instrument of oppression" conducting a "campaign to destroy democracy in Venezuela."

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Associated Press writer Jennifer Peltz in New York City and Alonso in Washington contributed to this report.