TALLINN, Estonia (AP) — A Moscow court extended on Thursday pre-trial detentions for three lawyers who once represented imprisoned opposition leader Alexei Navalny. The three were arrested in October on charges of participating in an extremist group, a case widely seen as a means to ramp up pressure on the politician.

The Basmanny District Court ruled that Vadim Kobzev, Igor Sergunin and Alexei Liptser will remain behind bars at least until March 13.

According to Navalny’s allies, authorities accuse the lawyers of using their status as defense attorneys to pass letters from the imprisoned politician to his team. Both Navalny’s Foundation for Fighting Corruption and a vast network of regional offices were outlawed as extremist organizations in 2021, a step that exposed anyone involved with them to prosecution.

Since January 2021, Navalny has been serving a 19-year sentence on charges of extremism. As President Vladimir Putin’s fiercest foe, he campaigned against official corruption and organized major anti-Kremlin protests. His 2021 arrest came upon his return to Moscow from Germany, where he recuperated from nerve agent poisoning that he blamed on the Kremlin.

Navalny has since been handed three prison terms and spent months in isolation in prison for alleged minor infractions. He has rejected all charges against him as politically motivated.

His team says that by targeting his lawyers, authorities are seeking to increase his isolation further. For many political prisoners in Russia, regular visits from lawyers — especially in remote regions — are a lifeline as it allows their families to know their lawyers have seen them, and also lets the prisoners report any abuse by prison officials.

The Kremlin has been carrying out an unrelenting crackdown on dissent in recent years, and ramped up pressure after invading Ukraine in February 2022. Since then and until early this month, 19,844 people have been detained for speaking out or protesting against the war while 776 people have been implicated in criminal cases over their anti-war stance, according to the OVD-Info rights group, which tracks political arrests and provides legal aid.

The case of Alexei Moskalyov, a 54-year-old single father convicted over social media posts criticizing the war in Ukraine, has drawn international condemnation. His lawyer and supporters say his troubles began after his teenage daughter’s anti-war drawing in school. He was sentenced in March to two years in prison; his daughter, after a stint at an orphanage, reportedly now lives with her mother.

Moskalyov lost his appeal in July, but a higher appellate court on Wednesday ordered a review of his appeal, citing “gross violations of criminal law” — a rare development in a country where judges most often side with the prosecution. It wasn’t immediately clear when a new hearing of the appeal would take place.

In addition to going after those who oppose the invasion, authorities have also actively targeted longtime Kremlin critics and human rights activists.

On Wednesday, a court in Moscow ruled to extend the arrest of Grigory Melkonyants, one of the leaders of Golos, a prominent independent election monitoring group, who was arrested in August on charges of involvement with an “undesirable” organization.

Golos was founded in 2000 and has played a key role in independent monitoring of elections in Russia. Over the years, it has faced mounting pressure from authorities. In 2013, the group was designated as a “foreign agent” — a label that implies additional government scrutiny and is widely shunned. Three years later, it was liquidated as a nongovernmental organization by Russia’s Justice Ministry.

Golos has continued to operate without registering as an NGO, exposing violations at various elections. In 2021, it was added to a new registry of “foreign agents,” created by the Justice Ministry for groups that are not registered as a legal entity in Russia. It has not been labeled “undesirable,” which under a 2015 law makes involvement with such organizations a criminal offense. But it was once a member of the European Network of Election Monitoring Organizations, a group that was declared “undesirable” in Russia in 2021.