Moscow (AFP) - Belarusian dissident Maria Kolesnikova has been returned to prison after being transferred to a hospital's intensive care unit last week and is being monitored by doctors, her supporters say.

The authorities arrested Kolesenkova and sentenced her to 11 years in prison last year, following massive popular demonstrations against the regime of President Alexander Lukashenko.

"Maria was transferred from Gomel emergency hospital to her prison at the end of last week," said a statement published by the media office of the opposition party, Victor Babariko.

Fears escalated following reports that Kolesnikova, one of the leaders of the unprecedented demonstrations, had been taken to the medical facility for treatment.

The statement said Kolesnikova would be under the supervision of doctors for at least 10 days.

The statement added that Kolesnikova's father "was able to see his daughter and confirmed that she was alive" during a 10-minute visit.

Babarikov's media office said Kolesnikova "has lost some weight and is still suffering from some weakness," adding that she was being treated for an ulcer.

Last Thursday, her supporters said she was "getting better".

Kolesnikova, 40, was one of three women who led the 2020 public protest movement in Belarus, along with Svetlana Tikhanovskaya, the presidential candidate to replace her imprisoned husband, and Veronika Tsepkalo.

The latter two fled the country under pressure from the authorities.

According to her relatives, Kolesnikova was kidnapped by the Belarusian special services and taken to the Ukrainian border for exile. However, she jumped out of the car window and tore up her passport, which led to her imprisonment.

The protest movement, which included thousands of demonstrators, was gradually suppressed, with thousands arrested, forced exile, and harsh prison sentences imposed on activists and journalists.