Venezuela's opposition says its leader María Corina Machado was briefly arrested and then freed after addressing a protest rally on the eve of President Nicolás Maduro's disputed inauguration.
Machado, 57, was "violently intercepted" in eastern Caracas and the motorcycle convoy in which she was riding was shot at, the opposition said, adding that she was forced to record several videos while being held.
Venezuela's information minister Freddy Nanez dismissed reports of Machado's detention as a "media distraction".
Maduro, 62, was declared the winner of last July's presidential election but the opposition and many countries, including the US, reject the result as fraudulent, and recognise the now-exiled opposition candidate Edmundo González as the legitimate president-elect.
González fled Venezuela in September and has been living in Spain, but this month he went on a tour of the Americas to rally international support.
The Maduro government has issued an arrest warrant for him, offering a $100,000 reward for information leading to his detention.
Machado, whom González replaced on the ballot after she was barred from running herself, has also been targeted. She went into hiding soon after the disputed elections, and was last seen in public in August before Thursday's rally.
Earlier in the day, the UN expressed its alarm after it received reports of arbitrary detentions and intimidation in Venezuela ahead of the opposition marches.
It highlighted the arrest of Carlos Correa, the head of an NGO promoting press freedom, who was seized by unidentified hooded men earlier in the week.
Maduro's government has deployed thousands of police officers in Caracas, where the government-allied National Assembly plans to swear Maduro in for a third term in office.
The opposition for its part urged its supporters to turn out in droves in an effort to thwart the ceremony.
In the city of Valencia, police fired tear gas at protesters, according to Reuters.
In western Caracas, 70-year-old Niegalos Payares told the news agency that "I'm not afraid, I lost my fear a long time ago".
And in the city of Maracay, in central Venezuela, Roisa Gómez told a Reuters reporter that she was "fighting for my vote, which I cast for Edmundo González. They cannot steal the election."
Maduro was declared the winner of the presidential election by the government-dominated National Electoral Council (CNE) but the CNE has to this day failed to provide detailed voting data to back up this claim.
Earlier this month in Washington, González met US President Joe Biden, who said that Venezuela deserved a "peaceful transfer of power".
In Panama, González deposited thousands of voting tallies which the opposition collected in the country's bank for safekeeping.
The tallies have been the key evidence offered by the opposition to show that González, not Maduro won the election.
With the help of official election witnesses, they managed to collect 85% of the tallies and uploaded them to the internet.
Independent observers and media organisations which reviewed them say they show González beat Maduro by a landslide.