The strongman leader of Russia's republic of Chechnya has derided international outrage about the arrest of a rights campaigner there.

Speaking on local TV late Wednesday, Ramzan Kadyrov referred to rights defender Oyub Titiyev as a "drug-addict" and mocked U.S. and European criticism of his detention.

Titiyev, the head of Chechen branch of the prominent Russian rights group Memorial, was arrested last week on drug possession charges he rejected. Rights groups called his arrest an attempt to silence criticism.

Masked attackers on Wednesday torched Memorial's office in the province in the region of Ingushetia, which neighbors Chechnya. The group believes the attack is linked to the crackdown on its work in Chechnya.