BUENOS AIRES/BRASILIA (Reuters) - An increasingly isolated Venezuela accused the Mercosur trade bloc of staging a "coup" on Friday after member nations suspended the socialist nation for failing to fulfill membership requirements.


In an official letter addressed to Venezuela's Foreign Minister Delcy Rodriguez and seen by Reuters, Mercosur informed Venezuela of "the cessation of the exercise of the rights inhered to a member state as of this date."


Following a decade in which strong growth and leftist policies across South America led the bloc to embrace Venezuela, the suspension now underscores the ideological split in a region struggling with plummeting commodity prices and enfeebled economies.


It further isolates the administration of Venezuelan President Nicolas Maduro, who is accused of exacerbating the political, economic and humanitarian crises battering the Andean country.


Rodriguez said she had not been notified in accordance with the rules of Mercosur and said Venezuela was the victim of "a coup at the heart of Mercosur."


"An illegal Mercosur is being born," she said at a press conference in Caracas.

Leaders of Mercosur, which also includes Argentina, Brazil, Paraguay and Uruguay, gave Venezuela a Dec. 1 ultimatum in September. They determined on Thursday that conditions had not been met for Venezuela to remain in the bloc, Argentina's foreign ministry said in a Friday statement.

To re-enter Mercosur, Caracas would need to renegotiate the terms of its membership in accordance with the bloc's economic, trade and immigration rules. Venezuela has told the bloc that some 130 norms, which include a human rights accord, are "inadmissible."

That signals any readmission talks could be tense and take years, said a Brazilian official involved in negotiations with Venezuela.

"They may not be able to reenter the bloc if there is something that goes fundamentally against Mercosur," said the official, who asked for anonymity to speak freely.

Venezuela entered the bloc in 2012.

Venezuela, home to some of the world's largest oil reserves, was seen then as a key trade partner by regional heavyweights Brazil and Argentina, both of whom had leftist governments allied with former Venezuelan President Hugo Chavez, Maduro's mentor and predecessor.

Although Venezuela is a big importer of Mercosur products, it has struggled to pay for them as its economy crumbled because of lower oil prices.

(Reporting by Alonso Soto; Additional reporting by Eyanir Chinea in Caracas and Caroline Stauffer in Buenos Aires; Editing by Alden Bentley and Andrew Hay)