Venezuela has arrested Antonio Ledezma, an opposition politician and metropolitan mayor of Caracas, in a move the government said was needed to halt a US-backed coup plot.
Men in camouflage uniforms forcibly entered the office of Ledezma, 59, in the Venezuelan capital on Thursday and carried him away.
An aide said some of the officers wore the uniform of the national intelligence service police.
Venezuelan President Nicolas Maduro announced that Ledezma would be punished for all his efforts to disturb the peace.
In a speech on Thursday night, Maduro said Ledezma had been "captured" and would face justice.
"He'll be held accountable for all his crimes," Maduro said in comments that TV and radio stations across the country were required to carry.
Last week, Maduro named Ledezma among a long list of government critics and Western powers accused of plotting a coup to bring down his socialist government.
Opposition leaders condemned the detention while residents of Caracas banged pots in protest and cars caught in traffic honked their horns.
Hundreds gathered in front of the headquarters of the intelligence service police to vent their anger.
Caught on video
Ledezma's arrest was captured on surveillance video. Men in black and grey camouflage can be seen pushing him from the building.
A member of Ledezma's security team, who was not authorised to give his name, said 10 men wearing the uniform of Venezuela's national intelligence service entered the building carrying guns and a hatchet.
They used their weapons to break the door to Ledezma's office, and then a dozen other men, wearing masks, came in and dragged the mayor away, he said.
Members of Ledezma's team gave statements on Thursday night amid the shattered glass of the office's front door. The rest of the office looked untouched.
Hector Urgelles, a spokesman for Ledezma's party, the Fearless People's Alliance, told the Associated Press news agency that the uniformed men did not identify themselves or give a reason for the arrest.
Urgelles said the party assumed Ledezma was being held by the national intelligence service in Caracas, but had no way to know for sure.
A statement posted on Ledezma's Twitter account earlier on Thursday afternoon said his office was full of government police.
'Like a dog'
An hour later, Ismael Garcia, an opposition politician, wrote on Twitter that Ledezma was carried off "like a dog".
Tensions have been running high in Venezuela this week with the one-year anniversary of anti-government street protests that rocked the country and resulted in more than 40 deaths.
The government arrested several other mayors and former mayors during last year's unrest, including Leopoldo Lopez, who is considered by human rights groups as Latin America's most prominent political prisoner.
Ledezma won election in 2008, beating a member of the socialist party led by late President Hugo Chavez.
The ruling socialist party subsequently transferred nearly all of Ledezma's powers to a newly created government entity.
Ledezma has long opposed the socialist leadership and a hunger strike he staged after federal authorities stripped his office of most duties made him a symbol for what the opposition calls the government's efforts to punish elected officials who do not fall in line.