Former San Cristobal mayor Daniel Ceballos was abruptly taken from his home before dawn by members of the Venezuelan intelligence services, his wife said on Twitter, posting a video of their vehicles as they drove away.
The Interior and Justice Ministry said intelligence services learned that Ceballos was getting ready to escape and "lead and coordinate violent acts around the country."
Patricia de Ceballos said her husband was loaded into an ambulance where he was shown an order transferring him to a prison in a distant state.
"The transfer of @Daniel_Ceballos to a prison constitutes one more link in a chain of human rights violations against prisoners of conscience," his lawyer, Juan Carlos Gutierrez, charged on Twitter.
Ceballos was the mayor of San Cristobal, a city in Tachira state near the border with Colombia, when he was arrested in March 2014, accused of inciting a nationwide wave of anti-government protests in which 43 people were killed.
He was moved to house arrest a year ago for medical reasons.
Ecuadorans expelled
Meanwhile, the Venezuelan foreign ministry confirmed the expulsion of a group of Ecuadoran lawmakers who had met in Caracas with opposition leaders, accusing them of "destabilizing" activities.
Cynthia Viteri, a member of the Ecuadoran Congress, said the group was intercepted Friday by government intelligence personnel outside a military prison where Venezuelan opposition leader Leopoldo Lopez is jailed.
"What we have lived through in #Venezuela was terrifying," she said Saturday, adding that the group had now arrived back home.
The incident comes amid rising political tensions as Maduro fends off pressure to hold a recall vote this year that could force him from office.
The opposition has called for a massive march on Caracas September 1 to press its constitutionally sanctioned demand for the referendum.
"Everything the government does is done to make people afraid, but the more outrages the government commits, the more people will march on September 1," said opposition leader Henrique Capriles, joining other opposition figures in condemning the decision to jail Ceballos.
Widespread food shortages, inflation topping 700 percent, a deep recession plus rampant crime have all fueled calls for a change after 17 years of socialist rule under Maduro and his predecessor, the late Hugo Chavez.
Viteri, who arrived in Venezuela on Thursday, had met with opposition leaders in the National Assembly and members of the main opposition coalition.
She and her group were waiting outside the Ramo Verde military prison to meet with Lopez's wife, Lilian Tintori, when they were picked up, she said.
The agents took their passports and told them they were being "expelled," she said.
Ecuador's foreign ministry said it was "concerned" about the incident and has asked the government for an explanation.
The Venezuelan foreign ministry charged that Viteri's group had "flagrantly" interfered in the country's internal affairs.
The Ecuadorans "engaged in proselytizing and destabilizing activities in a sovereign country, (which is) expressly prohibited by Venezuelan migratory norms," it said in a statement.
Human rights groups denounced the action against Ceballos, with Amnesty International calling it a "vile maneuver by the Venezuelan authorities to silence any critics amidst a growing political and economic crisis."
Jose Miguel Vivanco, Americas director of Human Rights Watch, demanded Ceballos's "immediate and unconditional" release.
