At least 50 people were killed by a teenage suicide bomber who blew himself up during morning prayers in a crowded mosque in Nigeria's Mubi town.A police officer said the dawn attack took place after the prayers at the mosque in Adamawa state. Pictures posted on social media in the aftermath of the attack showed bloodstains on the floor of the mosque, which had a gaping hole in its wall.Ahmed Musa, Chairman of Mubi council, said dozens of people had been injured but the exact number of casualties was not yet known as the wounded had been dispersed among several different hospitals.No group has claimed responsibility for the horror but Islamist militants Boko Haram typically target crowded places in northern Nigeria. The group has used children as young as five to carry out hundreds of attacks on busy marketplaces, checkpoints and mosques in the past few years.At least 45 people were killed in a suicide attack in the same state in December last year. In that attack two female suicide bombers detonated their explosives on a busy market.Boko Haram has been blamed for the death of more than 20,000 people and displacement of 2.3 million others in Nigeria since 2009.