At least 15 people were killed on Monday in a suicide attack in Nigeria's northeastern state of Borno, officials said.One security personnel said a suicide bomber detonated an improvised explosive device in Konduga, a central town in Borno, the state capital, Xinhua news agency reported.Terror group Boko Haram is suspected to be responsible for the suicide blast.Konduga was one of the areas invaded by Boko Haram in 2013. It was later liberated in 2015 by the Nigerian military.Boko Haram has killed more than 20,000 and displaced 2.3 million others since 2009.