He told a key meeting of state chief ministers that although the internal security situation had improved since February 2011, dangers remained.
Mr Singh said that “terrorism, religious fundamentalism and ethnic violence” needed to be tackled firmly.
Co-operation from states was necessary to combat such threats, he added.
“The so-called ‘protracted people’s war’ waged by the left-wing extremists against the state and society continues to target civilians and security forces, and economic infrastructure such as railways, mobile communications and power networks,” Mr Singh said in his inaugural speech at the conference on Monday morning.
“In the recent past, Maoists have also resorted to abducting foreign nationals,” the prime minister said, referring to the recent kidnapping of two Italian tourists in Orissa state. The hostages have now been released.
Mr Singh said 2011 was a better year than 2010 in terms of the number of deaths caused by Maoist rebels, but added there was still “a long way to go”.
The Maoist insurgency which began in the late 1960s has been described in the past by the prime minister as India’s “greatest internal security challenge”.