Masked men have torched the offices of a prominent human rights organisation in Ingushetia in southern Russia, days after the head of its operations in neighbouring Chechnya was arrested on hotly disputed drug charges.

Memorial, Russia’s oldest human rights group, published photographs of its charred offices in Nazran, the capital of Ingushetia, a republic in Russia’s volatile North Caucasus region.

The human rights group said that according to CCTV footage the attack happened early on Wednesday morning and was carried out by two masked men carrying petrol cans who climbed into a second floor window. The offices were empty at the time.

“Memorial considers this to be a terrorist act,” the organisation said in a statement. “There is clearly a link between this arson attack and those forces that are trying to destroy Memorial’s work in Chechnya and force Memorial out of the entire North Caucasus region.”

On 9 January, Oyub Titiev, the 60-year-old head of Memorial’s offices in Chechnya, was arrested and charged with possession of more than six ounces of marijuana. He faces up to 10 years in prison if found guilty.

Titiev, who took over at Memorial’s Chechen office after the murder in 2009 of his colleague Natalia Estemirova, has denied the allegations and said the drugs were planted on him by police. Human rights activists have said the charges are revenge for Titiev’s exposure of rights abuses by officials loyal to Ramzan Kadyrov, the Kremlin-installed leader of Chechnya. His arrest came shortly after Magomed Daudov, the speaker of the Chechen parliament, described human rights activists as “enemies of the people” and suggested they should be executed.

The US state department and the Council of Europe have both called on the Chechen authorities to release Titiev.

Titiev’s lawyer, Pyotr Zaikin, told Russian media this week that Chechen authorities had threatened to arrest the human rights activist’s relatives if he did not confess to the charges.

“If I confess, this will mean that I have been forced to plead guilty by means of either physical pressure or blackmail,” Titiev wrote in a letter to the Russian president, Vladimir Putin, that was published by Memorial.