MOSCOW — A Moscow court Wednesday declared the political and anti-corruption networks of jailed opposition leader Alexei Navalny "extremist" organizations, a move that will essentially crush the most formidable resistance to the Kremlin and force it underground.

The ruling, coming after an all-day closed-door hearing, effectively equates Navalny's political group and his Anti-Corruption Foundation with the Islamic State, al-Qaeda and the Taliban in the eyes of Russian authorities.

Navalny and his allies have long been barred from running for public office. But forcing the movement to disband marks a new, more aggressive chapter in Russia’s political repression.

Navalny’s team members could face six years in jail if they continue to work. Many have already fled the country. Donating to the organizations will be punishable by up to 10 years in jail. Retweeting previous videos by Navalny’s group, exposing the corruption of Russian politicians and bureaucrats, could also mean prison.

His 40 regional offices were disbanded in late April in anticipation of Wednesday’s decision.

But Ivan Zhdanov, the Anti-Corruption Foundation’s director, said in an interview with independent Russian news outlet TV Rain on Wednesday that “Navalny’s team will not stop its activities” and that the authorities “shouldn’t hope for that.”

The evidence used in the case was a state secret.

At the last hearing, on May 17, the attorneys defending Navalny’s organizations received six additional volumes of material from the prosecution. The court refused to let Navalny be called as a witness, the defense team, a legal rights group called Team 29, wrote on Twitter.

The legal team said it would appeal.

Navalny is serving a more than two-year prison sentence for charges he and international observers have said are politically motivated. He was poisoned last year with a lethal nerve agent, a hit on his life Navalny has said was carried out by state security agents acting on President Vladimir Putin’s orders.

His organizations’ popular investigations, published on YouTube, exposed graft in Putin’s inner circle.

Navalny’s team also coordinated an effort to weaken Putin’s United Russia ruling party with a system called “Smart Voting,” recommending supporters cast their ballots for candidates from other political affiliations.

Britain’s foreign secretary, Dominic Raab, called the court ruling “perverse.”

“It is another Kafka-esque attack on those standing up against corruption and for open societies, and is a deliberate attempt to effectively outlaw genuine political opposition in Russia,” said the statement from Raab.