Brazilian security forces staged an apparent controlled explosion at the Rio Olympics basketball arena on Thursday, forcing Spain and Nigeria to start their game in an empty arena. An explosion was heard just before the scheduled start of the game in Rio's main Olympic park. The blast also was heard at many neighbouring arenas. Security officials at the Olympic park had told AFP just before the explosion that there was a "special situation" that forced them to prevent a long queue of fans from entering the arena. Spanish and Nigerian players tipped off the game with no one in the stands, but fans were allowed in soon after that as security gave the all-clear. The game was not affected. A Rio 2016 spokeswoman at the arena declined comment on what exactly took place, saying Games organisers would issue a statement.