A suicide bomber has killed at least 16 people at a mosque in the Nigerian city of Maiduguri, police say. Dozens more were wounded in the attack.
It follows an overnight assault on the north-eastern city by Boko Haram, in which at least 13 people were killed before troops were able to push back the militants’ advance.
The attacks came hours after Muhammadu Buhari was sworn in as new president.
He has vowed decisive action against Boko Haram.
In recent years, the militants have killed thousands of people – mostly in north-eastern Nigeria – in its attempt to set up an Islamic state.
So far, no group has said it carried out Saturday’s suicide bombing.
Late on Friday, Boko Haram fighters fired rocket-propelled grenades into the southern suburbs of Maiduguri for around three hours.
The Nigerian army deployed armoured vehicles and fired back, forcing the militants to retreat.
The BBC’s Will Ross in Abuja says that the attack seems to be Boko Haram’s way of showing that they remain a significant threat despite a recent military offensive against them.
In his first speech as president on Friday, Mr Buhari reiterated his commitment to tackle the group, which he described as a “godless group, who are as far away from Islam as one can think”.
Mr Buhari, a former military ruler, has taken over from Goodluck Jonathan, who had been in office since 2010.
Nigeria’s new president has also promised that the government will do everything it can to rescue more than 200 Chibok girls who were captured last year by Boko Haram.
He is the first opposition figure to win a presidential election in Nigeria since independence in 1960.
Muhammadu Buhari in focus:
- Muslim from northern Nigeria, aged 72
- Military ruler of Nigeria from 1984 to 1985, deposed in a coup
- Seen as incorruptible
- Poor human rights record
- Survived apparent Boko Haram assassination attempt