Prime Minister Dr Manmohan Singh has said naxalism remains the biggest internal security challenge<br/>facing the country. Addressing his first national press conference after the UPA II took reins of power a year ago.<br/>Dr Singh said the government has not underestimated the problem of Naxalism. He said though law and order is a state subject but the centre will give all possible helps to states to tackle this menace.<br/> <br/><br/>