At least 15 soldiers were killed while 10 others sustained grievous injuries after Maoist rebels ambushed a patrol party in the Central Indian state of Chhattisgarh, police said Tuesday.Police said the member of Indian police and Indian paramilitary forces were part of a road securing party, adding, the patrol party was on its way of routine road screening when Maoist rebels triggered an Improvised Explosive Device (IED) and then opened indiscriminate fire with automatic rifles on the members of police and paramilitary officials near Tongpal area of Sukma district in Chattisgarh.The police said the killed include 11 members of paramilitary forces and four officials of the state police.The police said a helicopter has been pressed into service to evacuate the injured from the dense forest area.Senior paramilitary and police officials have reached the spot along with more reinforcements. The police said the search was going on to nab the rebels behind the attack.India's home ministry has already stated that Maoist rebels continue to pose major threat to the country's national security as they continue to target security forces and political leaders.The Maoist rebels are active in 83 districts spread across nine states of India.Maoist rebels have been fighting in several Indian states for more than 40 years claiming they have been inspired by the Chinese revolutionary leader Mao Zedong.Indian Prime Minister Manmohan Singh has already described the Maoist rebels as India's biggest internal security challenge.