Agents arrested Mayor Antonio Ledezma -- a well-known opposition politician -- on Thursday in a raid that sparked a fierce outcry from the president's political opponents.
President Nicolas Maduro said the mayor will be prosecuted "so that he answers for all of the crimes committed against the peace, security and constitution of our country."
In a televised address, Maduro said Caracas Mayor Antonio Ledezma was captured by order of the Attorney General's Office.
A high-level Venezuelan military source with knowledge of the situation told CNN en Español the mayor was taken into custody because of his alleged involvement in a plot to overthrow the government an accusation Maduro leveled last week
. Ledezma denied it, calling it the government's latest attempt to manufacture controversy and target political opponents.
His attorney, Omar Estacio, decried his detention. Ledezma was "virtually kidnapped," Estacio said, calling it "a violation of the most fundamental principles of Venezuelan law and international law."
The mayor's office told CNN en Español that more than 150 intelligence agents participated in Thursday's raid.
"They destroyed the doors," his wife, Mitzy Capriles, told CNN en Español. "There was no room for mediation. (My husband) was asking them to please stay calm and was asking what was going on. Abruptly, pushing and shoving, and without saying a word a gigantic, enormous contingent of agents, who were all over the place on the sixth-floor office where he works part of the day, took him away."
Richard Blanco, an opposition Venezuelan lawmaker whose office is also in the building, said he witnessed Ledezma's arrest.
"They pushed me as well and they pointed their guns at me," he said. "They broke the metropolitan mayor's office glass doors with a sledgehammer."
Opposition leaders said Ledezma was a political prisoner unjustly held by the government.
Word of his detention spread rapidly on social media after a Twitter post from the mayor's account Thursday evening said his office had been surrounded by police.
About 90 minutes later, another tweet from the account, purportedly written by the mayor's wife, said he had been beaten and detained without any arrest warrant.
"I hold Maduro responsible for the life of my husband," the tweet said.
Accusations of coup conspiracies have a long history in Venezuela. A coup briefly removed Chavez from office in 2002
In his national broadcast Thursday night, Maduro repeated accusations that his government had blocked a U.S.-backed opposition coup plot
that included plans to attack the presidential palace with a military jet.
"Enough already with vampires who conspire against peace," he said.
Maduro's accusations spurred a sharp response from the U.S. State Department, which called them "baseless and false."
"The United States is not promoting unrest in Venezuela nor are we attempting to undermine Venezuela's economy or its government. We remain Venezuela's largest trading partner," State Department spokesman Jen Psaki said in a statement Thursday night.
"Venezuela's economic and political problems are the result of the policies of the Venezuelan government. The Venezuelan government should stop attempting to distract attention from the country's economic and political problems and focus on finding real solutions through democratic dialogue among Venezuelans."
The accusations and the Caracas mayor's arrest come as opposition protesters mark the one-year anniversary of a wave of anti-government demonstrations that rocked Venezuela and led to the arrest of opposition leader Leopoldo Lopez.