British government officials have warned that attacks by extremists in southern Russia are very likely to occur during the Winter Olympics in February or the weeks before.
A threat assessment seen by the BBC says the Chechen separatist group led by Doku Umarov is the main threat, but so far the group has not targeted non-Russians.
The British threat assessment for the Games in Sochi is stark and says it will be taking place against a backdrop of violence in the region. It says Doku Umarov has called on followers to do whatever they can to disrupt the Games.
Police are hunting for a suspected female suicide bomber, but Sochi will not be an easy target.
Russia has sent in over 37,000 extra troops and police and placed a so-called 'ring of steel' around the Olympic venue.