Government and Congress Thursday rallied behind Home Minister P Chidambaram asserting his integrity is not in doubt even as the Opposition pressed for his resignation over his stand in the controversial 2G spectrum allocation.

Prime Minister Manmohan Singh also called Chidambaram from Frankfurt and is understood to have expressed full faith in his integrity, a day after a Finance Ministry note to the Prime Minister''s office(PMO) submitted to the Supreme Court by Janata party leader Subramanian kicked up a storm.

Both Chidambaram, who was touring quake-hite areas in Sikkim, and Finance Minister Pranab Mukherjee, who is in New York, declined to comment on the raging row over the "secret" note which appeared to have raised questions on Chidambaram's stand when he was the Finance Minister.

Mukherjee said he cannot make any remark on the matter as it is "subjudice".

"The matter is subjudice. I cannot make any comment on it. The whole matter is under the scrutiny of the Supreme Court of India. We cannot make any comment on any matter that is subjudice," he said.

The note suggested that the 2G scam could have been averted if the Finance Ministry, then under Chidambaram, had insisted on spectrum allocation through auction.

"The party does not doubt his integrity," Congress spokesman Abhishek Singhvi said rejecting the demand for Chidambaram's resignation or for a CBI probe in the light of the Finance Ministry note.

He said the "mischievous attempt" to create a rift between different constitutional functionaries is highly regrettable and ought not to be repeated.

Law Minister Salman Khurshid said there could be "no question mark" on Chidambaram and that he deserves the support of the government.

"I have now seen the paper and I want to make it very clear that as far as we are concerned in the government, there is no question mark whatsoever...nothing of questionable nature on the conduct of (then Finance Minister) P Chidambaram...I can say this with full authority. He deserves the support of the government," Khurshid said.

BJP's Murli Manohar Joshi, who as PAC Chairman probed the 2G scam, and AIADMK supremo Jayalalithaa led the Opposition offensive to demand that Chidambaram resign immediately or be sacked by the Prime Minister.

"The Finance Ministry officials were telling the then Finance Minister P Chidambaram to go for auctions. Why was it not done?.... There are clear contradictions here. I strongly demand that either Chidambaram should resign or he should be dismissed forthwith," Joshi said.

He further demanded that the "exact quantum of loss" to the country due to this scam should be determined by the present Finance Minister Pranab Mukherjee and made public. He said CBI should also inquire into the role of Chidambaram in the scam.

Joshi's colleague and senior leader Arun Jaitley also demanded a(CBI) probe into Chidambaram's role and said that the government, which is defending him is in denial. Jaitley also demanded Government's response to the Finance Ministry note.

The CPI-M backed the BJP demand, saying there is "mounting evidence" against him.

"It is quite clear that Mr Chidambaram is deeply involved in the 2G spectrum scam, which according to the CAG's report has caused a loss of over Rs 1.76 lakh crore to the Indian exchequer," Jayalalithaa said in Chennai in response to questions.

She said Chidambaram should immediately resign from his post or else the Prime Minister should drop him from the cabinet.

"The CBI should proceed against Chidambaram, as they did against A Raja...", she added.

DMK, a key UPA ally, utilised the Finance Ministry note to maintain that the stand taken by its MP and jailed former Telecom Minister A Raja on the issue has been 'vindicated'.

"The crux of the entire case is that Raja violated all advices by the Prime Minister and Finance Ministry. The letter (by Finance Ministry) says that the then Finance Minister had agreed to the fixed price, non-auction rule. This vindicates Raja's stand," top DMK sources said in Chennai.