MOSCOW — A human-rights activist in Chechnya has been detained by the police on drug possession charges in a case that colleagues and international observers say is part of a concerted effort to drive dissidents out of the Russian republic.

The activist, Oyub Titiev, 60, has run the Chechen branch of the Memorial Human Rights Center since the 2009 abduction and murder of another activist, Natalya Estemirova, a case that remains unsolved.

Chechnya’s Ministry of Internal Affairs reported on its website that the police found a plastic bag with what it said the police suspected was marijuana weighing about 180 grams when they stopped Mr. Titiev’s car for a document inspection on Tuesday. The drug possession offense is punishable by up to 10 years in prison.

The State Department on Wednesday called for the immediate release of Mr. Titiev, saying his detention was “the latest in a string of reports of alarming recent human rights violations in Chechnya.”