While Sochi's Olympic venues are now among the most tightly guarded facilities in the world, the rest of this sprawling Black Sea resort looks more vulnerable.
With about 100,000 police, security agents and army troops flooding Sochi, Russia has pledged to ensure "the safest Olympics in history." But terror fears fuelled by recent suicide bombings have left athletes, spectators and officials worldwide jittery about potential threats.
Security experts warn that Islamic militants in the Caucasus, who have threatened to derail the Winter Games that run from February 7-23, could achieve their goal by choosing soft targets away from the Olympic sites or even outside Sochi.
Some have raised the possibility that jihadists could have infiltrated Sochi long before security was tightened and have noted the vulnerability of the city's transport systems.
"The most daunting threat is suicide bombers," Grigory Shvedov, chief editor of the Caucasian Knot, an online news portal focusing on the Caucasus, told The Associated Press. He said 124 suicide attackers have struck Russia over the past 13 years.
Air defence missiles, drones, high-speed patrol boats and sophisticated sonars capable of spotting submarines, the array of high-tech gear deployed makes Sochi look like it's preparing for an enemy invasion from both air and sea.
Observers question, however, to what extent the Russian security agencies are prepared to respond to the most likely threat suicide bombers with primitive explosives strapped to their bodies.
The back-to-back December suicide bombings of a railway station and a bus in Volgograd, about 640 kilometers (400 miles) east of Sochi, killed 34 people and demonstrated the militants' ability to strike with shocking ease.
A jihadist group in Dagestan, the epicentre of the Islamic rebellion against Russia that has engulfed the Caucasus, claimed responsibility for the Volgograd bombings and has threatened to strike Sochi. Dagestan is only a few hundred miles (kilometres) from Sochi.
Police in Sochi issued leaflets recently warning about three potential suicide bombers, one of whom, a 22-year-old widow of an Islamic militant, was said to be at large in the city.
The notices have raised questions about efficiency of the rigid security measures in Sochi, which have involved the expulsion of thousands of migrant workers and blanket police checks of city residents.
Alexander Popkov, a Sochi-based lawyer who has defended local activists, said door-to-door searches in Sochi were conducted in two waves.
