New Delhi, Apr 30 (IANS): Prime Minister Manmohan Singh cannot escape accountability on the issue of allocation of coal blocks, the opposition said Tuesday as the government fought allegations that its top law officer had influenced the CBI probe on the case.

"Each passing day reinforces that the prime minister is not coming out clean before the apex court of the country. It is a very, very serious issue. He cannot escape accountability," Bharatiya Janata Party (BJP) spokesperson Ravi Shankar Prasad said after Additional Solicitor General Harin Rawal Monday blamed Attorney General G.E. Vahanvati for influencing the Central Bureau of Investigation probe into the irregularities in the allotment of coal.

"This government is embarrassment proof... let's not talk about embarrassment. We are deeply concerned about institutions," the BJP leader said.

"We will insist upon the accountability of the prime minister," he added.

"We have seen institutional integrity being compromised, CAG (Comptroller and Auditor General) being attacked, CBI being misused and now even the high office of attorney general has come under serious cloud. That is indeed a very sad moment," Prasad said.

CPI leader D. Raja echoed him and said the prime minister must own responsibility. He added that the position of Law Minister Ashwani Kumar had become "almost untenable".

The CBI last week told the Supreme Court that it shared its March 8 status report on investigations into coal blocks allocation with Ashwani Kumar and a senior bureaucrat in the Prime Minister's Office.

On Monday night, before the apex court bench headed by Justice R.M. Lodha was to take up for hearing the allegations of governmental interference into the investigation, Rawal is believed to have written a letter to Vahanvati levelling serious allegations against him.