Speaking after a visit to the region, Ms Arbour said she had "serious concerns" about the integrity of basic law enforcement institutions and warned there appeared to be no checks and balances on those in power.
Her view of life in Chechnya contradicted that of President Vladimir Putin, who regularly claims the republic is getting back to normal after more than a decade of separatist war.
Ms Arbour dismissed the assessment, saying allegations of police torture, intimidation, and disappearances were "credible" and serious changes were needed. "It is not credible to assume that people in Chechnya walk away from their homes without trace more than anywhere else in the world," she said.
"Chechnya has not been able to move from being a society that is ruled by force to one that is ruled by law." She added that police regularly use torture to extract confessions and anyone who complains about official wrongdoing is intimidated.
"When people complain about the brutality of the police they should not be intimidated but protected."
Ms Arbour suggested courts should force the police to video witness confessions to guard against brutality and disclosed that the UN would be appointing an official in Moscow to work on such projects.
Ms Arbour's bleak assessment of Chechnya is likely to displease Mr Putin. The President warned her not to politicise the issue of human rights but said his country was willing to work with human rights groups and did apparently concede there was a problem. Chechen human rights groups claim up to 5,000 people have "disappeared" since 1999 when Russian troops entered the republic.Reuse content