By Mayela Armas

CARABALLEDA, Venezuela (Reuters) - Venezuelan opposition leader Juan Guaido on Sunday said that President Nicolas Maduro's adversaries were "not afraid" even though he was briefly detained by intelligence agents, days after announcing he would be willing to replace the increasingly isolated president.

Guaido's comments on Friday spurred some opposition sympathizers to conclude that he had declared himself interim president, and led several government officials to say he should be arrested for treason.

Intelligence agents on Sunday pulled him from his car on the way from the capital, Caracas, to the coastal town of Caraballeda, his wife and opposition legislators said.

He was released shortly thereafter, they said.

"I want to send a message to Miraflores - the game has changed," said Guaido, 35, the head of the opposition-run congress, referring to the presidential palace, from a stage surrounded by cheering opposition sympathizers.

"Here we are! We are not afraid!"

The government said in a statement that it had identified four officers of the Sebin intelligence service who had acted in an "an irregular and unilateral manner" against Guaido as part of an "attempted media show."

"The officials involved are being rigorously investigated, have been suspended from their posts and will be subjected to the most severe legal and disciplinary sanctions," according to the statement read out on state television.

Guaido said the response was a sign that the government had lost control of its own security forces.

Asked whether he should be considered interim president, Guaido responded: "That has been clarified several times."

Venezuela's perennially fractured opposition has made numerous failed attempts over the past 20 years to remove the ruling socialists. Opposition leaders have called for a transition to a new government, but have not drawn up a clear plan for how to do so.

The U.S. State Department on Saturday had called on Venezuelan security forces to respect the "safety and welfare" of Guaido and other legislators.

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Maduro was sworn in to a second term on Thursday, defying critics in the United States and Latin America who called him an illegitimate usurper of a nation where economic chaos has wrought a humanitarian crisis.

A regional bloc, known as the Lima Group, that opposes the continuation of Maduro's leadership in Venezuela, said it condemned the "arbitrary detention" of Guaido. It added it would reject any pressure on congress or its members.

The once-booming OPEC member's economy has collapsed following the fall of oil prices in 2014. Inflation is close to 2 million percent and some 10 percent of the population has emigrated since 2015 in search of better living conditions.

Maduro says Venezuela is the victim of an "economic war" led by his political adversaries with the help of Washington. He insists the 2018 vote was legitimate and that the opposition boycotted it because it knew it would lose.

(Reporting by Mayela Armas; Writing by Brian Ellsworth; Editing by Peter Cooney and Grant McCool)