"We have some leads but it is too early to say which group is behind it", Singh told mediapersons accompanying him on his return from Dhaka to New Delhi.
Replying to a question about a sense of insecurity among the people since the 26/11 Mumbai terror attacks, he said the government had put in place several mechanisms and "innovative measures" but "there are obviously unresolved problems and weaknesses in our system and the terrorists are taking advantage of that".
"We must work hard to plug those weaknesses", he added.
The Prime Minister said he was confident that this is a war (on terror) that we will and must win."
He asked political parties to end mutual bickerings and mutual recriminations and work together to combat the problem of terrorism.
"I talked about cooperation with all political parties.
Instead of wasting time on mutual bickerings and mutual recrimination, I would ask all political parties, all shades of intelligent public opinion in the country to pool their knowledge wisdom and experience how we can tackle this (menace of terrorism)," he said.