(Confirms two dead, four injured) MOSCOW, Dec 9 (Reuters) - A blast on a bus in Russia killed two people on Sunday, Russian news agencies said, less than a month after five people died when a nail bomb exploded on a bus in a neighbouring province. Interfax quoted an unnamed source in the security services in the Stavropol region as saying the explosion may have been a "terrorist" act but may also have been caused by an exploding gas canister. Stavropol borders Russia's north Caucasus, a volatile region wracked by violence and centred around Chechnya, which has fought two wars against Russia since 1994. The bus had been travelling from the city of Stavropol to another town when an explosion started a fire on the bus while it was parked at a station. News agencies quoted the local emergencies ministry as saying two people had died in the blast and four more had been injured. On Nov. 22 a bomb tore apart a bus on the border of North Ossetia and Kabardino-Balkaria, an attack blamed on rebels. (Writing by James Kilner; Editing by Caroline Drees)
