A federal audit report said mobile phone spectrum licenses were sold at "unbelievably low prices," squandering an opportunity for the government to make $40 billion, the British Broadcasting Corp. reported Saturday.
Telecommunications minister A Raja has already resigned, denying he did anything wrong, and the Indian Supreme Court has demanded an explanation from the prime minister as to why Raja was not prosecuted earlier.
At a news conference, Singh said, "There should be no doubt in anyone's mind that if any wrong thing has been done by anybody, he or she will be brought to book."
He denied he failed to act in a timely fashion. Prime ministers, by law, have to clear prosecution cases against cabinet members.
Opposition Member of Parliament Subramanian Swamy said he called for the prime minister to act on the case in 2008.