Addressing a CBI conference on tackling corruption, he also asked probe agencies to tread cautiously when it was handling cases related to policy decisions.
Against the backdrop of the Gauhati High Court verdict declaring the agency as "unconstitutional", Singh said, "Our Government will look into this seriously and promptly. The Government will do all that is necessary to establish the need for the CBI and its legitimacy, and protect its past and future work."
The Supreme Court on Saturday had stayed the High Court order, saying accused in "sensational cases" have sought halting of the criminal proceedings based on the judgement.
Referring to public debate on corruption in the country, the Prime Minister said it is sometimes forgotten that economic growth also implies greater opportunity for corruption.
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"To keep pace with the aspirations of the people...Our government has taken several legal and administrative measures in the last nine years," he said.
Singh said investigations into cases of policy making and administration should be done with great care.