Abuja - Satellite imagery supports witness accounts that Nigeria's military bombed a refugee camp with "multiple air-dropped munitions," even though tents should have been easily visible, Human Rights Watch said on Thursday.The New York-based group again urged a thorough investigation of Tuesday's bombing of the camp that one Nigerian official said killed more than 100 refugees and aid workers. The Red Cross has estimated that 70 people were killed. Human Rights Watch said the dead included nine aid workers.Nigeria's military has said the bombing in the remote community of Rann in Borno state was an accident, saying it was trying to target Boko Haram Islamic extremist fighters.It is believed to be the first time Nigeria's military has acknowledged making such a mistake. The bombing has horrified the international community, with UN refugee chief Filippo Grandi calling it "a truly catastrophic event.""The Nigerian military has taken an important and rare step in accepting responsibility for this horrible attack," said Mausi Segun, senior Nigeria researcher for Human Rights Watch. "Now it should go further by explaining how it came to attack a displacement settlement, and by compensating the wounded and relatives of those who lost their lives."Nigeria's air force on Thursday said a panel of senior officers had been formed to investigate.The settlement, located near the border with Cameroon, houses thousands of people displaced by Boko Haram's insurgency, which has killed more than 20 000 people since 2009. The UN has called the humanitarian crisis in the region one of the worst in the world, with five million people at risk of starvation.The Red Cross said on Thursday it had evacuated nearly 90 people from Rann to the city of Maiduguri for "critical medical care."