An explosion aboard a bus in Russia's North Ossetia region has killed at least five people, including a nine-year-old girl, and hurt 12.
The bus was travelling from the city of Pyatigorsk and had stopped on the border with the Kabardino-Balkaria region when the explosion took place.
"It was an attack," a police official told AFP news agency.
Unrest linked to militants and criminal gangs is common in Russia's Caucacus republics bordering restive Chechnya.
The blast was caused by a device containing over 300g of explosives and loaded with nails and scraps of metal, police sources told the Reuters news agency.
As many as 19 people were on the bus, including two drivers, when the explosion took place.
Russian prosecutors have begun investigating the blast as a terrorist attack, according to the Interfax news agency.
A school in the town of Beslan in North Ossetia was the scene of a siege by militants in 2004, that left more than 300 people dead, most of them children.
Russians vote in parliamentary elections on 2 December, and authorities have warned of the possibility of terrorist attacks during the campaign.
On October 31, a bomb on a bus in the southern Russian city of Togliatti killed 8 people and left 50 injured.