An explosion at a train station in the southern Russian city of Volgograd has killed at least 13 people, reports say.
A suspected female suicide bomber killed at least six people when she attacked a bus in the city in October.
An Islamist insurgency in the North Caucasus region has led to many attacks there in recent years. Insurgents have also attacked big Russian towns.
Volgograd lies about 900km (560 miles) south of Moscow, 650km north of the North Caucasus and 700km north-east of Sochi.
‘Act of terrorism’
Sunday’s explosion rocked Volgograd-1 station at around 12:45 (08:45 GMT), shattering windows and sending plumes of smoke from the station entrance.
Ambulances rushed the injured to hospital, while footage from of the station’s entrance showed bodies laid out beside ambulances, with debris and shattered glass strewn on the station steps.
Interfax news agency quoted a source as saying the bomb was detonated near the metal detectors at the station entrance.
No group has yet claimed responsibility for the blast, which local officials said claimed at least 18 lives and left dozens more injured.
“Initial indications are that the blast was set off by a female suicide bomber,” said the National Anti-Terror Committee said in a statement.
In July, Chechen insurgent leader Doku Umarov posted an online video urging militants to use “maximum force” to prevent the Games from going ahead.
On Friday, a car bomb killed three people in the southern Russian city of Pyatigorsk.