Bombs have killed at least three people and wounded another 14 in north-eastern Nigeria.
There were two explosions at a hotel and one at a transport hub on Sunday night. A fourth occurred at a cattle market on Monday morning. One of those killed was a police officer.
Elections are to be held in Nigeria on Tuesday for the governors of 36 states.
Unrest swept across northern Nigeria following a presidential election on 16 April, which was won by incumbent Goodluck Jonathan, a southerner.
The BBC reports hundreds of people are believed to have been killed and thousands fled their homes.