Police in Belarus have made at least 100 arrests at protest rallies in the capital Minsk and other towns in the former Soviet republic.
In Minsk, they charged demonstrators near the presidential palace, firing pepper spray and wielding batons.
Tens of thousands of people rallied in the city for a protest against President Alexander Lukashenko.
They want the long-time president to resign after his re-election last month amid allegations of ballot-rigging.
Mass unrest since then has seen at least four people killed and hundreds injured as the government tries to stamp out dissent.
A number of opposition figures have fled the country, On Saturday, activist Olga Kovalkova became the latest to say she had taken refuge in neighbouring Poland amid threats of imprisonment.
Mr Lukashenko, in power since 1994, has accused Western nations of interfering.
Protesters, human rights activists and observers say riot police are brutally suppressing peaceful marches.
Belarus borders Russia, on which it depends heavily for energy and with which it historically has close ties, as well as Ukraine and EU states.
Lukashenko fails to stop protests once again
By Jonah Fisher, BBC News, Minsk
Sunday’s rally had several phases. The first was the tense and uncertain. Security forces had used razor wire to close off the obvious gathering points, Minsk’s main monuments and squares, and were standing guard behind them. Would-be protesters stood awkwardly on street corners wondering where and when the march would start.
Those in small groups were vulnerable and we watched as a man holding the outlawed red and white flag of the opposition was dragged into a car by security officers and driven away. Then, as the numbers grew, there were nervy stand-offs near Independence Square. As they grew in confidence the demonstrators approached, berating the riot police at the barricades that now blocked the road.
At about 16: 00 the crowd swelled exponentially as people marched out of the centre. This was no longer the brave early arrivals, it was Belarusians young and old. Some were in fancy dress, others wearing clothes that directly mocked the riot police, the Omon.
There were families, children, dogs – someone even brought a goose. For the fourth Sunday in a row President Lukashenko’s attempts to stop the protest against him failed.
What is the mood in Minsk?
After the Viasna non-governmental organisation reported 130 arrests on Sunday, the Belarusian interior ministry confirmed for Russian news agency Interfax at least 100 detentions across the republic.
Eyewitnesses told Interfax that police began to make arrests in Minsk after the unsanctioned rally ended and people were going home.
Video footage on Sunday shows men in plain clothes beating peaceful protesters with batons.
Sunday has become the key day for street demonstrations since the rallies began.
In recent days the security forces – dressed all in black with balaclavas over their faces – targeted university students as they returned from their holidays, dragging some from the streets and university buildings into unmarked minivans.
One protester in Minsk, who gave her name as Lyudmila, told the BBC earlier that the demonstrators were undeterred by the security forces.
“We are definitely not ready to get back to the life we had for many years now,” she said.
“We finally feel like we matter because we’ve been living in apathy for way too long and now we just have this feeling of solidarity and we actually think that – well, I feel personally that – changes already are happening so that’s definitely not the time to give up.”
Protests have also been reported in other Belarusian cities and towns including Grodno, Mogilev and Gomel.
What happened to Olga Kovalkova?
The activist said she had left for Poland as she would have faced a long jail term had she not agreed to leave Belarus.
Ms Kovalkova said security forces had driven her to a border post where she was able to board a bus to Poland after the driver recognised her.
A spokesman for Polish Prime Minister Mateusz Morawiecki said his country would offer support to victims of repression in Belarus.
Ms Tikhanovskaya, 37, represented the chief opposition to Mr Lukashenko in the election, entering the presidential race after her husband, Sergei Tikhanovsky, and another candidate were jailed.
She said the opposition was demanding an end to the police violence, the immediate release of all political prisoners, and a free and fair election.
How has the EU reacted to events in Belarus?
Last month, EU leaders agreed to impose sanctions – including asset freezes – on as yet unnamed Belarusian officials involved in alleged election-rigging, brutality and imprisonment of protesters. The exact sanctions are still being worked out.
The UN special rapporteur on Belarus, Anais Marin, said Mr Lukashenko’s re-election as president was “completely manipulated” and “people’s votes were stolen”.
She accused the Belarus police of torture, citing as one example a 16-year-old who was “so badly beaten up he was left in a coma”.
“The authorities must release all those arbitrarily arrested,” she said. “The government is waging an insane war against its own people.”
What is Lukashenko’s stance?
Mr Lukashenko has denied any allegations of vote-rigging. He has blamed some EU nations, in particular Poland and Lithuania, of trying to force regime change.
The 66-year-old has promised to defend Belarus.
On Thursday, he indicated he was open to moving closer to Russia, saying the protests had “prompted us to make relevant conclusions”.
On at least two occasions he has been photographed near his residence in Minsk carrying a gun and being surrounded by his heavily armed security personnel.