January 27 - Terrorist attacks in Russia before or during Sochi 2014 are "very likely to occur", British officials are warning.
The threat assessment for the Games, which begin 12 days' time, has reportedly been seen by the BBC.
Whitehall officials in London name a Caucasus group, Imarat Kavkaz, as posing the main danger at the Winter Olympics.
Last week, Islamic militants released a video claiming responsibility for the two deadly suicide bombings in Volgograd in December which killed 34 people and injured more than 100.
The video also threatened further attacks during the Olympics.
"If you hold these Olympics, we will give you a present for the innocent Muslim blood being spilled all around the world - in Afghanistan, in Somalia, in Syria, all around the world," the Russian-speaking men said during the 49-minute video.
"For the tourists who come, there will be a present, too."
Last summer, the leader of the Islamist insurgency Doku Umarov called for attacks aimed at undermining what he called the "Satanic Games" in Sochi.
The document produced by British officials reportedly acknowledges the huge security operation in and around Sochi - the biggest in Olympic history.
More than 30,000 police and Interior Ministry troops have been deployed, with measures to restrict vehicle access, the sale of firearms, explosives and ammunition now in operation.
Closed circuit television and surveillance drones will also be used to identify possible issues, while Russian President Vladimir Putin last month introduced additional anti-terrorism legislation into the Russian Duma.
This includes the introduction of prison terms of up to 10 years for those who receive training "aimed at carrying out terrorist activity".
FIB agents are also in the Winter Olympic host city to provide support to the Russians.
But while security will be undoubtedly high iother towns and cities in Russia could be seen as soft targets by terrorists wanting to disrupt the Games.
January 2014: Militants threaten more attacks in Russia as Sochi 2014 Olympic Torch reaches Volgograd region
January 2014: FBI agents to be sent to Russia to help protect US team during Sochi 2014
January 2014: Russia begins implementing biggest security operation in Olympic history with month until Sochi 2014
January 2014: Russia detains hundreds as Olympic world reacts to Volgograd bombings
December 2013: Second bomb in Volgograd kills 14 as IOC President condemns "despicable attack"