TALLINN, Estonia (AP) — Maria Kolesnikova, a prominent member of the Belarusian opposition serving an 11-year prison sentence for helping stage anti-government protests, was taken back to prison after undergoing an operation for a perforated ulcer, her father said Monday.

Alexander Kolesnikov was able to visit his daughter for about 10 minutes and found her weak but "her mood is good and she even tried to smile,” he told The Associated Press.

Kolesnikova, 40, has been in custody since September 2020 when she tore up her passport at the border to prevent her forced expulsion from Belarus amid massive protests challenging the reelection of the country’s authoritarian president Alexander Lukashenko.

She was convicted in September 2021 on charges of conspiring to seize power, creating an extremist organization and calling for action that threatened the security of the state.

Belarus was shaken by massive protests after the disputed August 2020 re-election of Lukashenko, which the opposition and the West denounced as a rigged sham. Authorities responded to the demonstrations with a massive crackdown that saw more than 35,000 people arrested and thousands beaten by police.

Kolesnikova helped coordinate opposition protests and resisted authorities’ attempts to force her to leave the country. When officers of the Belarusian security agency drove her to the border with Ukraine in September 2020 to forcibly expel her, she ripped up her passport and walked back into Belarus to face arrest.