The US and Latin American nations have voiced concerns over political tensions in Venezuela after the socialist government arrested the opposition mayor of Caracas for his alleged involvement in a coup plot.

Almost exactly one year after opposition figure Leopoldo Lopez was arrested as he led a wave of protests against President Nicolas Maduro, intelligence agents entered Antonio Ledezma's office late on Thursday and took him to jail.

A third radical critic of the government, Maria Machado, is under investigation over an alleged plan to assassinate Maduro, though she remains free.

Ledezma, 59, will be held in Ramo Verde prison, the same jail on the outskirts of the capital currently housing Lopez, officials said in ordering his continued detention.

The attorney-general's office earlier said Ledezma will be booked for his alleged involvement in a conspiracy "to organise and carry out violent acts against the government".

Henrique Capriles, opposition leader, called on the government to produce evidence of the supposed conspiracy.

"Does Maduro think that putting everyone in prison is going to get him 50 popularity points or that he's going to win elections?" the two-time presidential candidate asked.

'Baseless and false'

Ledezma's arrest led to spontaneous, if small, protests, with people banging pots after his arrest  onThursday night.

On Friday, fewer than 200 people attended a rally called by Machado.

Protests in recent weeks have been much smaller than last year. In late January, the defence minister authorised the use of "deadly force" to keep public order.

Maduro, who has accused the opposition of trying to topple him several times since his April 2013 election, said late on Thursday that Ledezma was detained over a coup plot financed by the US.

The US dismissed the "baseless and false" claims.

Maduro's turbulent year in power

The US condemned Ledezma's arrest, saying the "systematic intimidation" of opposition figures appears to be a bid by the government to divert attention from the country's political and economic challenges.

"Venezuela's problems cannot be solved by criminalising legitimate, democratic dissent," Jen Psaki, State Department spokesperson, said in a statement.

The top US diplomat for Latin America, Roberta Jacobson, called on Venezuela to free opposition leaders "as they have been unjustly imprisoned, and to improve respect for human rights".

Chile's socialist administration of President Michelle Bachelet voiced concern over the "polarisation in Venezuela, which could be a significant obstacle to dialogue between the government and the opposition".

Colombian centre-right President Juan Manuel Santos said "the latest events worry us" and that he hoped Ledezma would have "all the guarantees of due process".

The UNASUR South American bloc, meanwhile, is planning to hold an extraordinary meeting of foreign ministers on the situation in Venezuela.

Jose Miguel Insulza, secretary-general of the Organisation of American States, said Ledezma's arrest "has caused alarm" due to the way he was detained.

He called on the government to "stop those acts that lead to a spiral of polarisation that envelops Venezuelan society".

Signed advertisement

Ledezma was first elected in 2009, but many of his powers have been stripped by the central government over the years.

Last week, Ledezma and other opposition figures signed a newspaper advertisement calling for a democratic transition in Venezuela.

Maduro's popularity has fallen to 20 percent amid a growing shortage of basic goods, massive lines outside supermarkets and soaring inflation of almost 70 percent in the recession-hit country.

Jesus Torrealba, secretary-general of the MUD opposition coalition, said Ledezma's arrest amounted to a "coup from the state".

Maduro confirmed the mayor's arrest two days after visiting Cuba's retired leader Fidel Castro, a staunch ally since the days of late president Hugo Chavez.

Cuba's foreign ministry said it rebuffs "the economic and media war against the Bolivarian revolution and energetically rejects the statements and meddling actions of the United States and Organization of American States".

Source: Agencies