Venezuela defied international pressure over its deadly political crisis as European lawmakers accused its government of "brutal repression" and US President Donald Trump called the country "a mess."
Nearly a month of clashes at anti-government protests have left 28 people dead, according to prosecutors.
Venezuelan President Nicolas Maduro on Thursday intensified his row with foreign powers that he accuses of plotting to overthrow him.
His government announced it was launching the two-year process to pull out of the Organization of American States, a key regional diplomatic grouping whose secretary general Luis Almagro has branded Maduro a dictator.
"I am proud to say I took the decision... to free our country from interventionism," Maduro said in a speech on Thursday.
"We are free of the OAS and we will never return," he added. "To hell with the OAS! To hell with Luis Almagro!"
- OAS branded 'traitors' -
The move was a defiant show of force in a mounting crisis for Maduro, whose center-right opponents blame him for the country's economic collapse.
They want elections to remove Maduro, whose current terms runs through the end of next year.
The United States played down the announcement.
It "has no real practical or immediate effect because withdrawing from the OAS requires up to two years," State Department spokesman Mark Toner told reporters.
"In the meantime Venezuela will remain a full member of the OAS, and required to fulfill all of its obligations as a member state. And that begins obviously with respect for democratic norms and processes."
- Trump 'sad' for Venezuela -
US President Donald Trump meanwhile spoke out on the mounting crisis in Venezuela.
"Venezuela is a mess," he said in response to a reporter's question as he received Argentine President Mauricio Macri at the White House.
"I'm very sad for Venezuela," Trump said. "Venezuela is a very sad situation."
In Brussels, the European Parliament said in a resolution it "strongly condemns the brutal repression exercised by the Venezuelan security forces, as well as irregular armed groups, against the peaceful protests".
It urged the Venezuelan government to bring those responsible for the deaths to justice and guarantee the right to peaceful protests.
- US 'imperialism' slammed -
The OAS has led an international chorus of concern over the economic and political chaos in the major oil-exporting country.
Maduro has long had testy relations with the Washington-based regional group, calling it an instrument of US "imperialism."
But the final straw came on Wednesday, when 19 of the 35 OAS member countries voted to call a foreign ministers' meeting on the Venezuelan crisis.
A founding member of the OAS, Venezuela will become the first country to leave since the group was launched in 1948. Cuba was expelled in 1962.
Almagro had urged OAS members to sanction Venezuela for violating the group's democratic norms.
Political analysts questioned what Venezuela would actually gain by the move.
"Withdrawing from the OAS would isolate Venezuela much more and raise doubts about whether it remains a democracy," said Diego Moya-Ocampos of London-based consultancy IHS Markit Country Risk.
"This is without a doubt a desperate measure that indicates the government is trying to get out (of the OAS) before sanctions are applied," he told AFP.
- Injuries, arrests -
Venezuela has suffered an economic collapse fueled by a plunge in international prices for its crucial oil exports.
The center-right opposition planned further street protests for Thursday.
The opposition and government accuse each other of stirring up violence in the protests.
In just under a month of unrest, more than 400 people have been injured, and nearly 1,300 arrested, according to the attorney general.
Rights group Amnesty International urged the Caracas government Wednesday to stop the "persecution" and "arbitrary detention" of protesters.