MOSCOW — Before she knew that her father had been sentenced to two years in Russian prison because of antiwar comments he wrote on social media, 13-year-old Masha Moskalyova wrote him a letter.
Separated from her father, Aleksei Moskalyov, for almost a month after he was placed under house arrest and she in an orphanage — a punishment for opposing Russia’s war in Ukraine — Masha sent a letter to her father in court via his lawyer telling him to keep his spirits up.
“Hi Dad, I need you to stay healthy and calm,” Masha wrote in the letter, which was published by Mr. Moskalyov’s lawyer at his client’s request. It was brought to the court in Yefremov, 150 miles south of Moscow, where Mr. Moskalyov was sentenced in absentia to two years in prison. Officials said the father, who had been raising Masha alone for the past 10 years, had fled Tuesday morning before dawn.
On Wednesday, the independent Russian news organization Mediazona reported that a lawyer, Dmitry Zakhvatov, said that Mr. Moskalyov had been detained in Minsk, the capital of Belarus. That report could not be immediately verified.
Ms. Moskalyov’s posts on social media were brought to the attention of local authorities after Masha, then 12, drew a picture in school that showed Russian missiles targeting a mother and daughter holding a Ukrainian flag. “No to war,” she had written underneath.
In an example of the current level of censorship in Russia, both father and daughter were taken in for questioning the next day. They were also questioned by the Federal Security Services, or F.S.B., the primary successor to the Soviet’s fearsome K.G.B.
A European Union spokesman on Wednesday condemned the trial and the legal procedure against Mr. Moskalyov. The two-year sentence and the placement of Masha in an orphanage was “a total disgrace,” the spokesman, Peter Stano, tweeted. “Russia should respect its own constitution & intl obligations instead of punishing kids & parents for political reasons.” Mr. Stano had previously referred the case as demonstrating “Stalinist-like repression” that showed “another layer of the inhumanity of the Kremlin regime.”
In her letter, Masha also sought to remind her father of her confidence in his innocence.
“I love you so much and you should know that you did nothing wrong,” she wrote. “I’ll always be on your side and I believe everything you do is right. When you’re feeling bad or anxious, I feel sick and bad too. I believe that things are going to be fine and that we’ll be together someday. I hope for the best and love you so much.”
Memorial, one of Russia’s oldest and most prominent rights groups, which has also come under pressure from the Kremlin, said it considered Mr. Moskalyov a political prisoner.
“The criminal prosecution of Moskalyov is motivated by his political views and is aimed at the involuntary termination of civil activity of critics of the authorities and intimidation of the society as a whole,” Memorial said in a statement on Tuesday that referred to his daughter by her official name, rather than her nickname. “As a result, the right of his minor daughter Maria Moskalyova to live with her family has been violated.”
In the letter, Masha said she admired her father.
“I am proud,” she wrote. “Yes, Dad, I can say that I am proud of my father. A dignified, smart, handsome, unyielding man who loves his daughter so much.
“I love you, you’re a hero. My hero.”