Opponents of Venezuela president Nicolas Maduro poured into the streets to condemn the arrest of Caracas' mayor for allegedly participating in a US-backed plot to overthrow his government.
The protests came a day after an armed commando unit dressed in camouflage raided Mayor Antonio Ledezma's office and hauled him away.
The detention, recorded by security cameras, set off a wave of spontaneous demonstrations in middle-class neighbourhoods loyal to the opposition.
Yesterday a few hundred supporters gathered peacefully to denounce Mr Ledezma's "kidnapping".
The mayor was charged with conspiracy, a crime punishable by eight to 16 years in jail, and sent last night to a military prison outside Caracas where other prominent government foes are being held.
The arrest of the 59-year-old mayor, one of Mr Maduro's fiercest critics, comes as the government struggles to avert a crisis years in the making but made worse by a recent tumble in oil prices.
The president's approval rating was hovering around 22% last month, the lowest in 16 years of socialist rule, as Venezuelans are forced to cope with widespread shortages, runaway inflation and a plunge in the currency that shows little sign of abating.
Mr Maduro has taken to the airwaves in recent days to rail against his opponents.
He accuses them of conspiring with the US to sabotage the oil-dependent economy, sow chaos and carry out a coup timed to coincide with the anniversary this month of 2014 anti-government protests that left more than 40 dead.
As part of the crackdown, he has also seized control of a major retail chain, jailed several executives and handed more power to the military to control protests and smoke out saboteurs.
However, the dire situation has not translated into support for the frequently out-manoeuvred opposition.
Turnout at yesterday's demonstration was the largest for an anti-government rally in months.
But it was nowhere near the throngs that rocked cities a year ago, a sign of the steep challenge the opposition still faces connecting with mistrustful voters ahead of legislative elections later this year.
The government's case against Mr Ledezma appeared to stem from a public letter he wrote with two other hardliners calling for a transitional government.
Mr Maduro said the letter, published in an anti-government newspaper, was the green light for a secretly hatched putsch and yesterday said that next week he would present videos and recordings detailing US Embassy involvement in the plot.
The US called the accusations "baseless and false".
Mr Ledezma has been a thorn in the side of the ruling party since he was elected mayor in 2008, beating a member of the socialist party led by the late president Hugo Chavez.
The government subsequently transferred most of his powers to a newly created office run by a loyalist.
He was re-elected in 2013 and has been on the attack ever since alongside Leopoldo Lopez, a former mayor who he will now join in jail.
Mr Lopez was arrested a year ago for allegedly inciting violence at anti-government protests.