New Delhi: After former Comptroller and Auditor General or CAG Vinod Rai attacked Manmohan Singh on the 2G issue, Congress leader Kamal Nath today said the former Prime Minister may have made a "mistake" in not acting despite his letter to him expressing concern over the spectrum allocation process.

"He may have made a mistake. I would go along with you. I brought it to his notice. He did not understand the import and he did not act," Mr Nath said to a private news channel.

"I was disappointed that the Prime Minister did not act.... In retrospect and hindsight, the gravity and magnitude was not known. It was not known to me and the PM. It is very unfair to say that he knew everything," the former Union Minister and Singh's party colleague said.

His remarks came even as several Congress leaders defended Mr Singh on the 2G issue. The party too downplayed Nath's remarks and rejected the contention that the same had vindicated Rai's argument that Singh could not shirk responsibility for decisions to allocate 2G telecom spectrum and coal blocks.

Asked if things would have been different had Manmohan Singh acted differently, Nath said, "As recommended in my letter, if a group or a Cabinet Committee was set up, obviously the process would have changed. It required sharper and more focused attention".

"If it would not have been left to one minister alone, things would have been different," he told a private news channel.

Nath said that the CAG came much later and he had written the letter earlier. "We must understand that the CAG report came much later. We did not know that."

Nath dismissed the BJP's charge that 10 Janpath was involved and Sonia Gandhi told the Prime Minister to not pursue the matter.

"BJP is talking absolute rubbish. Sonia Gandhi, 10 Janpath did not know what was happening...Only the department knew what was happening not the entire government," he said.

Nath wondered that the CAG "never stumbled upon my letter, which was on record".

Replying to a question, he said, "I do not believe that the Prime Minister knew all the facts. I do not think he knew large parts of the facts."

At the All India Congress Committee or AICC briefing, party spokesperson Abhishek Singhvi rejected the contention that Mr Nath had vindicated Mr Rai's charge.

"Nath has said nothing of the sort what Rai said. It's a complete distortion to compare the two...Many people write letters, raise their concerns...Rai is speaking of complicity. Then he should have filed an FIR, become a witness...It is nothing but an exercise in self-advancement, self promotion," he said.