A prominent opposition leader in Venezuela has been jailed in a move that the government says was necessary to prevent acts of violence in the crisis-hit South American nation.

Daniel Ceballos, former mayor of San Cristobal, was sent to prison on Saturday, according to his wife and the country's interior ministry, after being told he was being taken for a medical exam.

His wife told the Associated Press new agency that Ceballos was put in an ambulance by people who said they were going to conduct a medical tests on her husband.

He was instead transported to a jail in central Guarico state.

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"They put him in an ambulance and showed us a notice of transfer to prison," she said in a video posted on her Twitter account.

The government said it had intelligence that Ceballos, 32, was planning to flee before the September 1 protests and carry out acts of violence.

"The compiled evidence will allow us to continue advancing in necessary investigations to prevent, uncover and neutralise any act that aims to destabilise our democratic system," the interior ministry said in a statement.

Ceballos was granted house arrest due to kidney problems last August after being held in prison for more than a year.

Venezuela President Nicolas Maduro has accused Ceballos and Leopoldo Lopez, another former mayor who was imprisoned in 2014 in connection with anti-government demonstrations, of being dangerous coup-plotters intent on toppling his government.

Ceballos' transfer to prison alarmed opposition and human rights groups.

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"Authorities in Venezuela seem to be willing to stop at nothing in their quest to prevent anyone from criticising them, particularly as the political and humanitarian situation in the country continues to deteriorate,” said Erika Guevara-Rosas, Americas director at Amnesty International.

The opposition has pledged a mass protest on Thursday to demand that authorities allow a recall referendum to go ahead.

A successful "yes" vote this year would cut short Maduro's term and trigger new elections.

But as Venezuela’s economy spins further out of control - with daily, lengthy food queues and inflation topping 700 percent - calls for Maduro's removal have grown louder, even among poor Venezuelans who still revere his predecessor and mentor, the late Hugo Chavez.

Electoral authorities, who are widely seen as bowing to Maduro's demands, say it is unlikely that a vote can be scheduled this year.

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Source: Al Jazeera News and agencies