A suicide car bomb outside police headquarters in the north-eastern Nigerian city of Maiduguri has killed at least five people, police say.
Following the blast, security forces in the city stormed a suspected hideout of the Islamist Boko Haram group, prompting a fierce gun battle, police sources told the BBC.
There is a huge security presence in Maiduguri, which is the stronghold of Boko Haram.
No group has yet claimed the attack.
However, Boko Haram - whose name means "No to Western education" - has targeted police stations, schools and other government buildings in the last 21 months.
The group wants to impose Sharia law across Nigeria.
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