A suicide bomber has detonated explosives at a northeastern Nigeria viewing center where soccer fans had gathered to watch the World Cup. Witnesses say Tuesday's blast in the town of Damaturu killed several people. Medical workers say scores of wounded people have been arriving at the main hospital in Damaturu, the capital of Yobe state. Witnesses say the bomber rode into the outdoor viewing center on a tricycle taxi and detonated explosives as people watched the match between Brazil and Mexico. There were no initial claims of responsibility for the blast. However, the northeastern states of Yobe, Borno and Adamawa have been under a state of emergency following a string of deadly attacks linked to the Boko Haram Islamist militant group. Last week, authorities in Adamawa and Plateau states ordered viewing centers closed because of a fear of possible attacks. Boko Haram militants have killed thousands of people during their five-year insurgency to establish an Islamic state in Nigeria's northeast, with attacks on schools, churches, mosques, bus stations and other public places.