For almost six months, Maria Kolesnikova has been hidden from the world.

Arrested in September 2020, the Belarusian opposition activist has been held in total isolation in prison in the country since last February, with no phone calls or letters and no visits from relatives or her lawyer.

"I wait for news every day… we don't even know if she's alive, really," Maria's sister, Tatsiana Khomich, told the BBC recently in Warsaw.

"I just hope this will not break her, but of course it influences anyone's mind in the end," she said, adding: "It could be considered as torture."

As the authorities in Belarus continue to track down and detain those involved in huge opposition rallies three years ago, they are also now holding the country's best-known political prisoners "incommunicado".

Sergei Tikhanovsky and Viktor Babaryko have vanished into the prison system, too, as well as other key figures from the opposition who are serving long sentences.

In 2020, both men attempted to run against the authoritarian Alexander Lukashenko for president, but were arrested.

"I think they want to break them, mentally," is how Tatsiana explained the isolation now of prominent detainees like her sister.

"They see they are still optimistic and very strong, and they want to break this mindset."

Maria Kolesnikova was one of a trio of women who rallied crowds in nationwide protests after Mr Lukashenko claimed yet another landslide election win.

The reaction was like nothing Belarus had ever seen.

The protests against a rigged vote ended in mass arrests, beatings and torture - all thoroughly documented, but still flatly denied by officials.

Maria stood out, not only for her bleached-blonde crewcut and bright red lips, but for the constant smile they formed and her defiantly positive attitude.

It was that spirit that made her rip up her passport when the authorities tried to deport her - and that got her arrested.

The last Tatsiana heard from her sister was a postcard from prison dated 2 February 2023.

Maria wrote of longing for the old, free days when she would drink an abundance of coffee and discuss new projects with friends. But she drew a smiley face and a heart, assuring Tatsiana she was "fine", her mood "more upbeat and impassioned".

Since then, there's been no word.

Alexander Lukashenko has repeatedly claimed there's "not one" political prisoner in Belarus, because there's no such article in the criminal code.

But the respected human rights group Viasna currently lists almost 1,500 people imprisoned for their peaceful political actions or views.

One of its own activists, just released, was made to spend his last nine days in solitary confinement, sleeping on a damp concrete floor and using his fist for a pillow.

"Three political prisoners have died in prison, so it can be crucial for at least someone to see them," Natalia Satsunkevich told me from Lithuania, where the Viasna activist now lives for safety.

She recalled the artist Ales Pushkin who died recently in custody with the official cause still unknown.

"He'd lost a lot of weight. So it would have been obvious," Natalia suggested.

And the arrests haven't stopped.

At a women's shelter in Warsaw, Inga described how police came for her two years after the protests were crushed.

They had found photos of her on a friend's phone, including one from a rally where she was wearing the red and white opposition flag like a cape.

"They said, if you're 'political', then you'll feel it," Inga said, as she recalled her week at Okrestina detention centre in the Belarusian capital Minsk.

There were 14 women in a cell with four beds; no showers, toothbrushes or toilet paper.

"They treated us like animals," she added.

But that isn't the memory that makes her cry. It's when she remembers moving to pre-trial detention and realising that everyone in her cell was there for their politics.

"We had state TV and it talked as if nothing bad was happening," Inga said. "And we were like, how can you say it's all OK, when so many people are in prison?

"I didn't know people were being imprisoned in such numbers. Then you get there and everyone's political. It's a nightmare," she confided, crying quietly. "We're sent to prison, just for our words."

Sentenced to house arrest, Inga fled the country earlier this year with the help of activists. She didn't tell her son where they were going until they were safely in Europe. She couldn't risk him revealing the secret.

She now joins a rally in central Warsaw every Sunday to sing Belarusian songs, remember other political prisoners and chant against the war their country is helping to wage on Ukraine.

Only a handful turn out, although the number of Belarusian exiles in Poland is growing all the time.

"I think that's a betrayal," organiser Anna Fedoronok told me. "If we forget all the people in prison, then we're betraying them."

"We're free here. If we don't speak out, who will?"

She and a friend now film skits for social media: they dress up as elderly women, in headscarves and housecoats, contorting their faces and cackling into the camera.

They prop a framed photograph of Mr Lukashenko on the sofa behind them, like an icon.

The women are fighting a repressive regime by laughing at it.

"I have no other weapon," Anna said. "Should I just sit here and wait for change? I can't."

When prominent opposition figures like Maria Kolesnikova were handed long sentences, their supporters tried to remain positive: Alexander Lukashenko couldn't last in power that long, they reasoned.

So the prisoners would soon be freed.

Instead they're being punished further, with isolation.

"They want to make people forget them, so we don't speak about them," Tatsiana Khomich believes.

"They want to get back to life as usual, as if they never tortured people or sentenced them to 10 or 20 years," she added.

"But they can't succeed in that."