ussian prosecutors on Monday asked a court to sentence a top rights activist in Chechnya to four years in a penal colony over what campaigners say are trumped-up drug charges.

Oyub Titiyev, the 61-year-old head of the Chechnya branch of rights group Memorial, was arrested at the start of last year.

His lawyers say the case is connected to Titiyev’s investigations into the secretive prison system of a republic that is notorious for rights abuses.

“We ask that Titiyev be found guilty and sentenced to four years in a penal colony, along with a fine of 100,000 rubles ($1,500, 1,350 euros),” prosecutors told a court in Chechnya, according to Russian news agencies.

A verdict in the trial, which has been ongoing since last summer, is expected shortly.

Observers say drug charges have been used repeatedly in the past to silence critical journalists and rights workers in the region.

In a statement on Monday, Amnesty International called for Titiyev to be “released immediately and unconditionally”.

“Amnesty International believes Oyub Titiyev is a prisoner of conscience, imprisoned solely for his work for the victims of human rights in Chechnya,” the rights group said.

Memorial is the last rights organisation to retain a visible presence in Chechnya while remaining critical of local leader Ramzan Kadyrov.

The group said its offices in the neighbouring Ingushetia republic were torched following Titiyev’s arrest and colleagues in Dagestan, another Caucasus republic, were attacked.

The group speaks out about human rights violations in Russia and has accused the Chechen leader of overseeing a “totalitarian” regime that uses kidnappings and torture.

Titiyev’s predecessor as the regional leader of Memorial, Natalya Estemirova, was kidnapped and killed in 2009. The rights group said the killers were acting on the orders of local authorities.