A Russian court found the imprisoned opposition leader Aleksei A. Navalny guilty of fraud and contempt of court on Tuesday, opening the door to a sentence of as much as 13 additional years in prison.
The sentence was expected to be announced later in the day at Mr. Navalny’s trial, which was being held in a makeshift courtroom at the prison outside Moscow where he has been held for more than a year.
“Navalny committed fraud, that is, the theft of other people’s property through deceit and breach of trust,” the judge, Margarita Kotova, said in reading her verdict, according to the news agency Interfax.
Prosecutors claimed that Mr. Navalny and his former Anti-Corruption Foundation — which the Russian authorities banned as extremist last year — embezzled people’s donations.
The verdict, however, was widely seen as a move by the Kremlin to keep Mr. Navalny behind bars beyond the expiration of his current two-and-a-half-year prison term, ostensibly for violating the terms of his parole, in 2023.
For President Vladimir V. Putin, the war against Ukraine has made the fiery opposition leader even more of a liability. Mr. Navalny has been urging Russians, via letters from jail that his lawyers post to social media, to protest the invasion.
“It is every person’s duty to fight against this war,” Mr. Navalny said in a courtroom speech last week. The war, he said, was started by a “group of crazy old men who don’t understand anything and don’t want to understand anything.”
Even with Mr. Navalny in prison, his aides outside Russia have been calling for protests against the war and continuing to publish their trademark corruption investigations on YouTube. On Monday, the group released a video that offered evidence that Mr. Putin was hiding a $700 million yacht at a dock in Italy.
Another video from the group said that during Mr. Navalny’s trial last week, Judge Kotova had received multiple phone calls from a number that researchers traced to the head of public relations for the presidential administration.
“The case was entirely fabricated by specific people,” Ivan Zhdanov, the former head of Mr. Navalny’s foundation, says in the video. “This verdict is being written by Putin’s officials.”
Judge Kotova has not commented on the allegations, but she was promoted to a more senior judicial position last week, the state news agency RIA Novosti reported.
Mr. Navalny’s backers sometimes say that the exact length of his prison term matters little, because they expect Mr. Putin’s system to collapse in the coming years.
But for the moment, Mr. Putin has the upper hand. The Kremlin has forced Mr. Navalny’s network of supporters into exile and, in recent weeks, blocked access to Instagram and Facebook, and cracked down further on the independent media — making it ever harder for Mr. Navalny to communicate with the Russian public.
There is substantial evidence that the Russian government was responsible for the poisoning that nearly killed Mr. Navalny in August 2020, and with the world’s attention on Ukraine, Mr. Navalny’s supporters fear that his life is in danger again.
The latest verdict could allow the Russian authorities to move Mr. Navalny to a higher-security prison farther from Moscow, making it harder for his lawyers and family to visit him.
“Without public protection, Aleksei will be face to face with those who have already tried to kill him,” his spokeswoman, Kira Yarmysh, posted on Twitter on Monday. “And nothing will stop them from trying again. Therefore, we are now talking not only about Aleksei’s freedom, but also about his life.”