A bus caught fire and exploded in Russia's troubled North Caucasus Thursday, killing at least four people and wounding 11, emergency and police officials said. Investigators considered terrorism the likely cause. The bus traveling from the southern city of Pyatigorsk was near a police post on the administrative border of the North Ossetia region when the fire broke out, said Oleg Ugnivnenko, a spokesman for the regional Emergency Situation Ministry. The explosion happened shortly after. One child was among those killed, he said. Federal Security Service and Interior Ministry investigators on the scene consider terrorism to be the likely cause, Ugnivnenko said. The RIA-Novosti news agency, citing an unnamed law enforcement official, said the blast may have been caused by an explosive device in the road.