A Venezuelan opposition leader, Leopoldo Lopez, has handed himself over to the National Guard after holding a speech to thousands of his supporters.
He said he hoped his arrest would wake up the country to its "unjust justice".
It comes as several thousand of pro- and anti-government supporters took part in tense rival rallies in the capital, Caracas.
Mr Lopez was wanted on charges of inciting violence during recent street protests which left at least four dead.
Speaking before thousands of his supporters wearing red, President Nicolas Maduro said Mr Lopez would be brought to Justice.
"He must answer before the prosecution, the courts, the laws his calls to sedition, his unawareness of the constitution," Mr Maduro told the crowd.
Tensions have been running high in the deeply polarised country.
Three of the dead - two anti-government protesters and one government supporter - died of bullet wounds sustained during demonstrations last Wednesday.
Another student died after being ran over during a march on Monday night in the eastern city of Carupano.
Before handing himself over to the authorities, Mr Lopez denied the charges against him.
"I present myself to an unjust judiciary. They want to jail Venezuelans who want peaceful, democratic change," he said.
Ahead of the rallies, Caracas Mayor Jorge Rodriguez warned that he had not authorised Tuesday's opposition march.
Police and members of the National Guard were out in force. Opposition activists have accused the authorities of trying to prevent them from attending the anti-government rally.
The anti-government demonstration was called by Mr Lopez, leader of the opposition Popular Will party and former mayor of Chacao district in eastern Caracas.
Earlier, he urged his supporters to join the march but asked them to stop short of the Interior Ministry, which is located in a pro-government area of Caracas and where he was planning to hand in a petition.
"I will walk alone. I won't put any Venezuelan lives at risk. Go Venezuela!" he wrote on Twitter.
The BBC's Irene Caselli in Caracas says thousands of people - many wearing white and holding Venezuelan flags - gathered in the east of the city in support of Mr Lopez.
Government supporters wearing red held a rival march and headed to the presidential palace for the meeting with President Maduro.
It appears Mr Lopez took the decision not to lead his supporters into the path of the pro-government protesters, our correspondent adds.
In a video statement released on Sunday, Mr Lopez said he had not committed any crime and insisted allegations that he had incited violence were untrue.
The US state department earlier denied claims that it was helping to organise the anti-government protests.
"The allegation that the United States is helping to organise protesters in Venezuela is baseless and false," spokeswoman Jen Psaki said.
Her statement came a day after Venezuela announced it would expel three US diplomats for allegedly meeting students who had been leading marches.
The main opposition grievances are high inflation, crime and the shortage of some staples.
The government has blamed the shortages on "saboteurs" and "profit-hungry corrupt businessmen".