The latest bombing, in the capital on Saturday, left at least 22 people dead and led some local media to accuse the government of incompetence and failing to implement a comprehensive strategy to deal with terrorism.
However, Singh dismissed the accusation that the government's policies had put the country at an increased risk of attack.
"There is no question of government being soft on terrorism," he said.
Critics have said that India's police are massively understaffed and under-resourced, noting that there is no central database of anti-government suspects and little time for meticulous investigations.
"There is no question of government being soft on terrorism"
India's prime minister
Madhukar Gupta, India's top-most home ministry official, said on Thursday that policing at state level would be overhauled with separate units focused on intelligence gathering and analysis.
India has previously focused much of its intelligence activity on neighbouring Pakistan, but several of this year's bombings have been claimed by a little-known group calling itself the Indian Mujahidin.
Singh insisted that the role of Pakistan-based groups should "not be minimised", while also acknowledging that the apparent involvement of local fighters added "a new dimension to the terrorist threat".
P. Chidambaram, India's finance minister, warned that there was a growing sense of "alienation" among the around 140 million Muslims in the Hindu-majority country.
"The divide between the Muslims and Hindus is taking new and dangerous forms," he said in a speech on Wednesday. "Out of the hopelessness and despair ... will rise new waves of terror."