Police said a motorcycle bomb went off in a market area on Tuesday. The rider was killed and two employees of a nearby shop were injured.
"We are investigating whether the victim was himself a terrorist or a passerby," said city police chief Pervez Rafi Bhatti.
Another blast was heard a short time later in the city, but the cause was not immediately known.
About 90 minutes earlier, a bomb planted near the railway tracks just outside the city injured four people including a policeman, a guard and an electrician on a train. The identity of the fourth person was not immediately known.
The device went off as the Jaffar Express crossed a bridge in the suburb of Saryab, senior police officer Hamid Shakil said.
"The bomb was detonated by a remote control device," he said. It went off with a deafening sound, damaging a staff coach at the front of the train, he added.
"It is an act of sabotage and the aim was to create terror"
Police officer Hamid Shakil
The policeman, guard and the electrician were injured by glass shards, Shakil said, adding that passengers on the train bound for the northern city of Rawalpindi escaped unhurt.
"It is an act of sabotage and the aim was to create terror," he said.
The rail blast was the fourth in two weeks to hit the line in Baluchistan, which borders Afghanistan and Iran.
The blasts come amid an increasingly violent rebellion by separatist tribesmen, who are demanding better royalties and more jobs from local natural resources.