Russia said on Friday it had detained six men suspected in a bombing in the southern city of Pyatigorsk last month that killed three people.
A security alert is in place before the 2014 Winter Games which begin on 7 February in the Black Sea resort of Sochi, some 270km west of Pyatigorsk where the car bomb went off on 27 December.
The federal anti-terrorist committee said the six men had admitted carrying out the bombing and that they were planning another attack on a larger scale.
Two bombs killed at least 34 people on 29 and 30 December in the city of Volgograd, about 700km northeast of Sochi.
