Romanian police say they are investigating 188 people over nationwide anti-lockdown demonstrations.
Protesters took to the streets in several Romanian cities on Monday night against new pandemic measures that came into force a day earlier.
Around 1,000 people gathered in the capital, Bucharest, to march through the central Victory Square and chant "freedom'' outside the government headquarters.
"We have identified 188 people," police spokesman Ionel-Catalin Stegaroiu told a press conference on Tuesday.
As many as "12 police officers were injured, three of them were taken to hospital, although they have not been admitted."
One man was detained by police in Bucharest after refusing to identify himself when he was called out for not wearing a face mask.
Police estimate that they have issued fines totalling 200,000 lei (€40,000) for breaches of anti-COVID measures.
Amid rising coronavirus infections, Romania's government brought forward the start time of a nightly curfew to 8 pm and ordered shops to close at 6 pm.
But hundreds of protestors gathered in Bucharest, Constanta, Pitesti, and Ploiesti, at 10 pm to block traffic and rally against the curfew.
The protests were largely organised on Facebook by accounts critical of the government's handling of the pandemic, including the far-right AUR Party.
Party leader George Simion, who has called on people to protest across the country every day this week, attended the Bucharest demonstration.
AUR has also previously called for demonstrations against vaccination and other measures to curb the spread of the coronavirus.
On Monday Romania recorded nearly 1,400 COVID-19 patients in intensive care units - its highest number since the start of the pandemic.
Around 12,000 others are also receiving regular hospital care for the virus.