A bombing at a Nigerian shopping mall in the capital city Abuja left 21 people dead and 17 wounded Thursday.
It is the latest in a series of violent attacks blamed on Islamic extremists.
Two separate explosions in April killed more than 120 people and wounded about 200 at a busy bus station in Abuja.
Both attacks were claimed by Boko Haram, which has since threatened more violence.
More than 2,000 people have been killed in Boko Haram attacks this year. The Muslim insurgent group is seeking to establish an Islamic state in northern Nigeria.