One of the last remaining high-profile opposition figures in Belarus, Maxim Znak, has been detained by masked men, his supporters say.
Mr Znak, a lawyer and member of the opposition Co-ordination Council, failed to show up for a scheduled video meeting on Wednesday morning.
Witnesses reported that he had been led down a street in the capital, Minsk, by masked men in plain clothes.
Several other opposition figures were recently detained in the country.
Maria Kolesnikova, one of three women who joined forces to challenge President Alexander Lukashenko in August's election, is currently in detention after she resisted attempts by the authorities to expel her to Ukraine.
She is the last of the three women leading the opposition to remain inside Belarus.
Mr Znak, meanwhile, is believed to be the last active member of the Co-ordination Council inside the country. The body was set up by the opposition to oversee a transfer of power after the disputed election.
The vote triggered mass protests amid allegations of vote-rigging.
What happened to Maxim Znak?
The 39-year-old, who previously worked as a lawyer for jailed presidential candidate Viktor Babaryko, was due to take part in a video call on Wednesday but failed to dial in.
When a colleague called him, Mr Znak said someone had arrived and then hung up.
He then texted the word "masks" to a group, one activist told local media. This is believed to be a reference to the face masks worn by the Belarusian security services.
Witnesses then reported seeing Mr Znak being led down a street close to his offices by masked men in civilian clothes.
On Monday, Mr Znak spoke to the BBC about his concerns for his safety.
"I'm pretending to be relaxed," he said. "It's a professional habit – but actually I'm very concerned and scared."
The police are yet to comment on reports of his detention.
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