Singh said everyone must unequivocally send out a message that pursuit of violence cannot be justified under any circumstances and reaffirm the collective resolve to fight the menace of terrorism in all its forms with available means.
"The problems of terrorism and Left-wing extremism constitute two major challenges that our society and polity face today. The terrorist attack in Delhi last Wednesday is a stark reminder to us that there can be no let up in our vigilance," he said addressing the National Integration Council (NIC) meeting here.
The meeting was attended by senior Union Ministers, Chief Ministers, Leaders of Opposition in Parliament, leaders of national and regional political parties among others.
"Time and again our nation has been subjected to terrorist violence. Terrorist seek to justify such violence based on misplaced sense of ideology," he noted.
The Prime Minister said no civilised society can tolerate or endorse loss of innocent lives in the pursuit of any ideology and institutions and instruments of the country's democratic polity allow sufficient opportunity for articulating differing view without resorting to violence.
Singh stressed on the need to identify and address the causes of radicalisation of some of the country's youth.
"Very clearly, lack of productive employment opportunities for our young men and women is one factor which aids such radicalisation. Education and skill development opportunities have a major role to play in addressing this problem," he said.