Prime Minister Manmohan Singh on Wednesday admitted that Naxalism flourishes in under-developed areas but made it clear that urgent and considered action will be taken against those challenging the authority of the State.

Addressing the Civil Services Day function here, he asked civil servants to devise innovative ways to ensure that the benefits of government's ambitious development programmes reach the people.

Describing Left-wing extremism as the gravest internal security threat faced by the nation, he said, "Recent events have underscored the need for urgent and considered action to root out this problem".

"No quarter can be given to those who have taken upon themselves to challenge the authority of the Indian state and the fabric of our democratic polity," he said.