WASHINGTON (Reuters) - The U.S. State Department said on Wednesday it was troubled by the reported arrest of human rights activist Oyub Titiev in Russia’s Chechnya republic and it urged authorities to immediately release him and allow nongovernmental groups to operate free of harassment.

Titiev, who runs the office of the Memorial Human Rights Centre in Chechnya, was arrested on Tuesday by police who said they found a substance in his car that smelled like marijuana, an allegation that other rights activists said sounded like a set-up.

“Given well-founded concerns about potential mistreatment of Mr. Titiev in custody, we urge Russian federal authorities to ensure that Mr. Titiev’s rights are protected in accordance with the Russian constitution and Russia’s human rights obligations,” State Department spokeswoman Heather Nauert said in a statement.