ABUJA, Nigeria — Two car bombs detonated in Nigeria's capital Friday and a third explosion hit a venue where the president was celebrating the nation's 50 th independence anniversary, leaving at least seven dead following a threat from the country's main militant group. The explosions came after militants warned there was " nothing worth celebrating after 50 years of failure" in Africa's most populous nation, which is oil-rich but where most live on less than $1 a day. Friday's attacks would be among the militants' boldest yet, striking in Nigeria's capital during an event with heavy security held hundreds of miles (kilometers) from the Niger Delta region where they are based. A car bomb detonated just as a military formation began to march at Eagle Square, where President Goodluck Jonathan was on hand for the Five minutes later, a second car bomb detonated, killing at least seven people, a police officer told an Associated Press reporter at the scene. At least one of the dead was a policeman, the officer said. The officer spoke on the condition of anonymity, as he was not authorized to speak