ABUJA, Nigeria — Two car bombs blew up on Friday as Nigeria celebrated its 50th independence anniversary, killing at least seven people in an unprecedented attack on the capital by suspected militants from the country's oil region.The Movement for the Emancipation of the Niger Delta, the main militant group in the country's oil-rich southern delta, had threatened to attack the festivities and warned people to stay away."For 50 years, the people of the Niger Delta have had their land and resources stolen from them," the group said in a statement. While Nigeria, Africa's most populous nation, is oil rich most people live on less than $1 a day. The delta is very impoverished and polluted from spills.A third and smaller explosion hit a venue at Eagle Square where President Goodluck Jonathan stood with other dignitaries, about a 10-minute walk from where the car bombs detonated. A security agent was apparently injured in that explosion.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 delta.The car bombings seemed designed to lure first-responders and then kill them with a second blast. Five minutes after the first vehicle exploded, the second went off, 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 because he was not authorized to speak to reporters.