Prominent Belarusian activist Olga Karach, who heads a human rights center in Vilnius, said Lithuania had denied her asylum request on Friday.
The decision was taken by Lithuania's migration department on the basis of intelligence assessments, she said.
"The state security department said that my actions could pose a threat to Lithuania's national security. This is nonsense," she told AFP.
Karach is the head of the Lithuanian-based NGO "Our House" which provides humanitarian aide to Belarusians in Lithuania and at home. It also monitors the human rights situation in Belarus.
Having secured residence permits in Lithuania since 2014, Karach relocated fully to the country in 2020.
The activist said Lithuanian authorities had pointed to a 2021 interview with Russian MP Vladimir Zhirinovsky and her participation in conferences in Russia as factors contributing to their assessment.
But Karach stressed that the interview had been unfavorable to Zhirinovsky, a right-wing ultranationalist who died in 2022.
The conferences she attended were organized by EU entities before relations with Moscow deteriorated over its invasion of Ukraine, she added.
The activist said she would appeal the decision, including to the European Court of Human Rights if need be.
Contacted by AFP, the migration and state security departments refused to comment on the decision to deny her asylum.
Deportation does not appear to be an immediate threat however as her residence permit is still valid.
Karach said she had sought asylum because she wanted to avoid detention while travelling abroad.
"If I go to some country, and (Belarusian President Alexander) Lukashenko puts me on Interpol (for arrest), I can simply be detained there," she said.
In 2021, the Belarusian KGB designated Karach as a "terrorist", and last year, the Minsk government classified her organization as an "extremist" entity.
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