Nigerian President Goodluck Jonathan has visited the site of what is believed to be the country's first suicide bombing, which killed a policeman and wounded at least seven other people.
After his inspection Friday, the president urged Nigerians not to panic, saying "terrorist attacks" are affecting countries all over the world.
The radical Islamist group Boko Haram claimed responsibility for Thursday's blast outside Nigeria's national police headquarters in Abuja. The explosion was so powerful that it destroyed more than 30 cars.
Authorities blame the group for a string of deadly attacks in Nigeria's north that have targeted police officers, government officials and other authority figures.
Also Thursday, a bomb went off in Nigeria's northeastern Borno state, killing four children. Police said the children were playing nearby when the bomb went off inside a home in the town of Damboa. There was no immediate claim of responsibility.
Nigeria experiences frequent bomb attacks, stemming from political and sectarian tensions.
Boko Haram is believed to have carried out many bombings and shootings in Borno state. The group is pushing to impose strict Islamic law across the north.
Boko Haram launched a brief uprising against the government in July 2009, sparking a heavy military response and a week of fighting that killed some 700 people.
Some information for this report was provided by AFP.