Published by New York Times

The abrupt arrest of the Caracas mayor on accusations he plotted an American-backed overthrow of the government threatened to plunge Venezuela into new political convulsions on Friday, as his supporters rallied in the capital and pockets of protest erupted elsewhere.

The arrest of the mayor, Antonio Ledezma, carried out Thursday evening by intelligence agents who fired weapons in the air, was viewed by the opposition as the kidnapping of a political rival to President Nicolás Maduro.

Mr. Ledezma’s backers called it another assault on democracy in Venezuela, the oil-endowed nation that has been reeling from a severe economic decline under the watch of an increasingly unpopular president.

Many opposition figures said Mr. Maduro, desperate to divert attention from Venezuela’s internal ills and his own disapproval ratings, concocted Mr. Ledezma’s arrest.

Mr. Maduro, the protégé of Venezuela’s longtime leader Hugo Chávez, often castigates the United States, accusing it of attempting to topple his government.

He promised, in a nearly three-hour speech soon after the mayor’s arrest, to release evidence to demonstrate what he called the secret American plot to topple him.

“Every fascist has his day,” said Mr. Maduro.

“I have heard them saying that this is a lie, this is a show,” Mr. Maduro said, speaking of his political adversaries. “Because the United States gave the order, you have to mock the accusation, it must be trivialized. This is serious.”

Mr. Ledezma’s lawyer, Omar Estacio, met with his client soon after the arrest. “He’s content, in a happy state of mind and not scared of anything,” said Mr. Estacio, adding that Mr. Ledezma, 59, had sensed something was awry.

“He started to be followed around two weeks ago by cyclists, black cars et cetera,” said the lawyer. “He had a feeling therefore that something like this would happen.”

Mr. Estacio and other witnesses described the method of arrest as disproportionately severe. They said Mr. Ledezma had been working calmly in his office when a dozen armed officials came, fired into the air, and dragged the mayor away to the intelligence agency’s Helicoide headquarters.

Mr. Maduro confirmed that the mayor would be dealt with by Venezuela’s judicial system on what he described as charges committed against the country’s “peace, security and constitution.”

A hard-line opposition figure and ally of Mr. Ledezma, María Corina Machado, was charged in December in a plot to assassinate Mr. Maduro.

“If anyone in Venezuela knows about coup-plotting, it’s Mr. Maduro and those in power right now,” said Ms. Machado, referring to a failed coup attempt by Mr. Chávez in February 1992 which the government here continues to celebrate.

The United States government has repeatedly denied Mr. Maduro’s accusations. “These latest accusations, like all the previous such accusations, are baseless,” read a statement from the State Department.

“The United States is not promoting unrest in Venezuela nor are we attempting to undermine Venezuela’s economy or its government,” the statement read. “Venezuela’s problems cannot be solved by criminalizing dissent.”

Venezuela is the fourth largest provider of crude oil to the United States. Many government critics suggested Mr. Ledezma’s arrest was a means to silence the opposition before legislative elections to be held later this year. The opposition is able to call for a recall referendum in 2016.

Gladys Ramírez, a lawyer who attended a Friday rally against the arrest, said the mayor had been detained because he is the type of leader who can push the government out of office. “This government has lost all perspective,” Ms. Ramírez said. “This isn’t democracy. We’re suffering a dictatorship.”

María Martínez, a 68-year-old retiree, said the government was trying to put a stranglehold on the opposition. “The opposition has been kidnapped, and so the people have been kidnapped. We’ve all been kidnapped,” she said. “I don’t know if this is a dictatorship, communism or what. But it’s not a democracy.”

Mr. Ledezma’s arrest came nearly precisely a year after the detention of Leopoldo López, a hard-line opposition figure who was once touted to be the country’s next president. Mr. López remains in jail on charges of inciting major nationwide unrest a year ago.

Mr. López’s father, also called Leopoldo, attended the Friday rally for Mr. Ledezma. “It’s not about my son. It’s about Venezuela,” he said. “This latest arrest demonstrates that we have a tyrannical government in power.”

The collapse in the international price of oil, from which Venezuela derives nearly all foreign income, is an important reason for the economic ills. Annual inflation was at 69 percent in 2014. The country’s currency has fallen more than 50 percent in value against the dollar on the black market in the last year. And shortages leave supermarket shelves across the country nearly empty and queues stretching sometimes into the thousands.

“The government is showing force and generating fear, “ said Luis Vicente León, director of Datanálisis, a data polling firm, which has calculated Mr. Maduro’s approval ratings in the low 20 percent range.

Mr. Maduro’s unpopularity, combined with the troubled economy, is raising fears of major unrest like that seen early last year, which was supported by Mr. López, Ms. Machado and Mr. Ledezma. Tens of thousands took to the streets and pitted themselves against authorities in battles involving Molotov cocktails, rubber bullets and tear gas.

Mr. Ledezma is not the first opposition mayor to find himself detained. Daniel Ceballos, mayor of San Cristóbal, near the country’s border with Colombia, was detained in March on similar charges to Mr. López last year.

“All us Venezuelans that express views differing from those of Nicolás Maduro have our days numbered,” said David Smolansky, opposition mayor of nearby the El Hatillo municipality. “The question is when the guillotine falls.”

María Eugenia Díaz contributed reporting from Caracas, and Frances Robles from Mexico.