Sofia Sapega, a Russian citizen who was detained along with Belarusian journalist Roman Protasevich after their flight was diverted to Minsk on Sunday, may face criminal charges in Belarus, Russia's Foreign Ministry said on Tuesday.

Belarus on Sunday scrambled a warplane to intercept a Ryanair passenger jet carrying Protasevich, a journalist critical of Belarusian leader Alexander Lukashenko, in an act denounced by Western powers as "state piracy".

Sapega, a 23-year-old student who was travelling with Protasevich, was detained by Minsk "in connection with the suspicion of having committed, between August and September 2020, offences under several articles of the Belarusian Criminal Code," a Russian Foreign Ministry statement said.

Belarusian authorities have extended Sapega's detention for two months, TASS news agency reported, citing her father, Sergey Dudich.

Sapega is a student at a university in the Lithuanian capital Vilnius. She was flying there with Protasevich after their vacation in Greece to defend her master's thesis ahead of graduation, according to the university.

Furious Western powers prepared on Tuesday to heap sanctions on Belarus and cut off their aviation links with the former Soviet republic in response to the diversion of the Ryanair flight and arrest of Protasevich.

His social media feed from exile has been one of the last independent outlets for news about Belarus since a security crackdown on mass protests against authoritarian President Alexander Lukashenko's rule after a disputed election last year.

Regular demonstrations in Minsk started in August with protesters who wanted Lukashenko to quit after an August 9 election they said was rigged to give him a landslide victory.

About 35,000 people have been detained since then and protests have subsided.

Sapega was detained on Sunday, and on Tuesday her lawyer was told she was being held for two months.

The 23-year-olds mother said her daughter was innocent and simply in the wrong place at the wrong time.

She steered clear of politics, her mother Anna Dudich told Reuters in an interview on Tuesday.

Speaking from the Belarus town of Lida, Dudich said she feared for her daughter's health and safety in detention.

"Of course, this is the main thing which I fear now," she said. "She is a very tough girl in a moral sense. She will get through, she will withstand, I'm sure of that."

Neither Dudich nor the lawyer have been able to contact Sapega since her detention, and have not been informed of any charges against her.

"My hopes are now probably based on a miracle and on the knowledge that my daughter is definitely not guilty of anything," Dudich said. "She simply showed up in the wrong place at the wrong time."

Dudich said she had not spoken to Protasevich, 26, and that her daughter had been in a relationship with him for less than six months.

A passenger on the diverted flight told Reuters that, as Protasevich realized he was about to be arrested, he handed Sapega his laptop and phone for safekeeping.

"She was a very good student," Dudich said. "She had very ambitious plans."

On the eve of the flight, her daughter called Dudich to tell her about her Greek vacation. Then she sent one final text after the plane was forced to land in Belarus.

"In Minsk she just wrote me 'Mama'. And that was it."

Reuters