Accusing Prime Minister Manmohan Singh of protecting "tainted ministers", the Bharatiya Janata Party (BJP) yesterday asked him to take action against Home Minister P Chidambaram over his apparent links with the spectrum pricing controversy.

"Let heads roll if need be," Leader of Opposition in Lok Sabha Sushma Swaraj told a news conference, a day after the prime minister, on his return from the UN, defended Chidambaram.

At a joint press conference along with her Rajya Sabha counterpart Arun Jaitley, Sushma Swaraj also defended the BJP against charges of trying to force early elections.

In a direct and hard attack on Manmohan Singh, the party accused him of closing his eyes to reality and failing to lead the nation. Pointing out that both Manmohan Singh and Congress president Sonia Gandhi had May 22 vowed to fight corruption, Sushma Swaraj asked, "How did the policy of fighting corruption become a policy of saving corrupt ministers?"

Jaitley said the prime minister was expected to protect the truth, not "a tainted minister".

Chidambaram has been embroiled in a row since a note from the finance ministry hinted that he too was to blame for the spectrum pricing decision that has landed former communication ministers A Raja in jail.

Sushma Swaraj insisted that "para after para" of the note sent to the Prime Minister's Office proved that Chidambaram, as then finance minister, was aware of pricing of 2G spectrum allocation.

She also berated the Central Bureau of Investigation (CBI), which she derisively dubbed as the "Congress Bachao Institution", for declaring that there was no need to probe Chidambaram in the spectrum issue.

Meanwhile, Finance Minister Pranab Mukherjee has written a fresh letter to Prime Minister Singh on the controversial note by his ministry that said the 2G spectrum could have been auctioned had the then finance minister Chidambaram acted, officials said.

A copy of the three-and-a-half page letter has been sent to Congress President Sonia Gandhi too, party sources said.