A team of India’s top anti - terrorism investigators and security experts has launched an investigation into a recent deadly ambush by Maoist rebels in the central state of Chhattisgarh, officials say.Indian officials say six-member National investigation Agency team held several meetings with the police and senior administration officials in the troubled region on Tuesday. Sources say hundreds of police are also scouring forests for the rebels in the Darba town where two dozen people, including some top state politicians, were killed in the surprise attack on Saturday. . The investigation comes days after Indian Maoist rebels launched the attack on a convoy of cars carrying local leaders and supporters of the ruling Congress Party. At least 24 people died and several others sustained severe injuries in the deadly ambush. Local sources in the volatile region say the assailants blocked the road, set off a mine and began firing at the convoy. The rebels, who are supported by tribal groups and landless farmers, have fought against state and central government for many years. Thousands of people have died in the Maoist-related clashes over the past three decades. The Maoist militancy has now spread to 20 of the 28 Indian states. India's Prime Minister Manmohan Singh considers the Maoists as the gravest threat to the country's internal security.