At least 50 people were killed and hundreds injured in multiple blasts in Nigeria's Borno state, officials said on Monday.Security sources said the first explosion was targeted at a mosque in Ajilari area of Maiduguri at the time of the late evening prayers on Sunday, Xinhua news agency reported.Another bomb is said to have exploded in Gomari area and the third explosion occurred at a game centre where people pay to play computer games and charge their mobile phones.The three blasts come a day after a new audio message purportedly from Boko Haram leader Abubakar Shekau accused the army of lying about successes against the militants.Reacting to the audio message, Sani Usman, Nigeria's military spokesperson, described Shekau's comments as "the rant of a drowning man", adding that efforts were on to ascertain if it was indeed Shekau's voice in the audio clip.The military spokesperson added that the attacks signify a high level of desperation on the part of the Boko Haram terrorists.