Maiduguri - A suicide bomber pretending to be a madman blew himself up on Thursday and killed at least five people outside government offices in Nigeria's northeastern city of Maiduguri, witnesses said.
Another six people were wounded, the witnesses said, speaking on condition of anonymity for their safety.
Many more could have died but guards prevented the seemingly demented man from entering the complex, they said.
Ambulances with blaring sirens rushed to the scene in the bustling downtown area which was cordoned off by soldiers.
Residents blamed the incident on Boko Haram Islamic extremists who have killed hundreds this year in suicide bombings.
Thursday's blast comes the day after worshippers prevented a suicide bomber from entering a mosque on the outskirts of Maiduguri, the birthplace of Boko Haram and headquarters of the Nigerian military's campaign against the jihadists. The military said the bomber blew himself up and wounded four people.
The two bombings this week are the first attacks in two months, indicating the success of heightened vigilance by soldiers and self-defence groups that have reported intercepting several suicide bombers recently.
The last reported suicide bombing in Nigeria was a March 16 attack by two women who killed at least 24 worshippers during dawn prayers in another mosque on the outskirts of Maiduguri.
The decrease in attacks, which were an almost daily occurrence earlier this year, also marks the success of a military campaign that officers say has Boko Haram on the run and hemmed into strongholds in the Sambisa Forest, a sprawling game reserve 45 minutes' drive southwest of Maiduguri.
Dozens of Boko Haram fighters are surrendering, reporting shortages of food and ammunition, the military said this week.
About 20 000 people have died and 2.1 million made refugees in Boko Haram's nearly 7-year uprising to create an Islamic state.