(http://news.bbcimg.co.uk/media/images/81270000/jpg/_81270697_nigeriabiu4640215.jpg) More than 50 people died in Tuesday's attacks in Kano and Potiskum but no group has said it carried them out.
Boko Haram still controls much of the north-eastern Borno state and has displaced more than three million people.
The rising violence has already led to the postponement of February's presidential elections, with the vote now due to take place on 28 March.
Source: BBC