Russia has launched one of the biggest security operations in Olympic history a month before the start of the Winter Games in the Black Sea resort of Sochi. The authorities are deploying more than 30,000 police and interior ministry troops and limiting access to the area. The main concern is the threat of attack by Islamist militants from the restive North Caucasus region. Russia's most wanted man, the Chechen rebel leader Doku Umarov, has urged his fighters to target the Winter Olympics.