KURCHALOY, Russia (AP) — A court in Russia's province of Chechnya has sentenced a prominent rights activist to four years in prison on drug charges widely seen as an effort by the authorities to stifle a critical voice.

The court in Chechnya's city of Shali sentenced Oyub Titiyev to four years in penal colony on charges of drug possession he has denied as fabricated. His lawyers said they would appeal the verdict.

Titiyev has been in custody since his arrest in January 2018 in what has been largely perceived as a vendetta against a rare critic of the Chechen government. As the head of the Chechen office of prominent rights group Memorial, he played a major role in exposing extrajudicial killings, kidnappings and torture perpetrated by security forces in Chechnya.

Chechen leader Ramzan Kadyrov, who previously dismissed rights activists as liars and traitors, publicly called the 61-year-old Titiyev a "junkie." Titiyev's supporters said the case aimed not only to silence the activist, who is known as a devout Muslim, but also discredit him in the eyes of the community.

Amnesty International's director for Eastern Europe and Central Asia, Marie Struthers, denounced the verdict as "an affront to human rights, reason, and justice."

"By pronouncing him guilty, despite all the evidence to the contrary, the court has demonstrated how deeply flawed the Russian justice system is," Struthers said in a statement. "The court has revealed itself to be little more than a tool that the regional authorities have used to silence one of the last human rights defenders working in Chechnya."

She charged that the federal authorities "proved to be accomplices in this gross injustice" by failing to heed the rights defenders' demands to transfer proceedings out of Chechnya where she said the court was unable to give Titiyev a fair trial because of pressure from regional authorities.

"We call on the Russian authorities to immediately and unconditionally release (Titiyev) as he is a prisoner of conscience, imprisoned solely for his human rights work in Chechnya," Struthers said.

Titiyev's 72-year-old sister Zharadat Titiyeva said that the prosecution aimed not only to silence her brother, but also to smear his reputation as a devout Muslim who doesn't drink or smoke, let alone take drugs.

"They decided to disgrace him in front of the people: Look who your defender really is: he's just a junkie," she said at the family's home in the village of Kurchaloy, about 35 kilometers (22 miles) away from regional capital Grozny,

Titiyev's wife and three children fled Russia after he was jailed. His eldest daughter still lives in Chechnya.

The Chechen leader last year pledged unhindered access to hearings in the Titiyev case, but vowed to make Chechnya after the end of the trial a "no-go zone" for human rights activists whom he described as being no better than "terrorists and extremists."