"A hundred police were using drugs according to the results of tests that were launched almost a year ago. Almost all of them have been fired," city police chief Sergei Umnov told the regional legislature.

Almost 30,000 police work in the northwestern port city and its surrounding region, a police spokesman told AFP.

Russia's vast police force is dogged by cases of violent crimes committed by officers under the influence of alcohol and is widely feared by the public.

Russia has between 2.5 and six million drug addicts, and more than 100,000 people die each year as a result of drug use, according to official figures.

Due to its proximity to Afghanistan and its porous borders, Russia is among the world's top three heroin consumers along with Iran and Pakistan, according to the drugs control agency.