NEW DELHI  - India's opposition called the government the "most corrupt since independence" on Tuesday as a row over political interference in a police probe escalated in the Supreme Court.

The top court rebuked the nominally independent Central Bureau of Investigation (CBI) for showing the government a report on its investigation into alleged corruption in coal mine allotments. Government lawyers had denied in court that the results of the probe into the scandal, which is being monitored by the Supreme Court, were shared with politicians before the judges. "The very foundation of the investigating process is shaken by political interference," the Supreme Court said.

The court's statements brought renewed opposition calls for Premier Manmohan Singh's resignation and marked the latest in a string of political embarrassments for his scandal-tarnished Congress government.

The CBI, whose report on what the media calls "Coalgate" is still to be made public, has been probing charges by the auditor last August that the government may have given away $33 billion in windfall gains to firms to mine coal.

Singh, in addition to being prime minister, was coal minister for much of the period under police scrutiny. Both Law Minister Ashwani Kumar and officials of Singh's office were shown the report "at their desire", the CBI admitted to the Supreme Court last week, adding "changes were made" without revealing them publicly.

"This has been the most corrupt government since independence" of India in 1947, said Sushma Swaraj, leader of the opposition Bharatiya Janata Party, which walked out of parliament in protest on Tuesday.

While the opposition did not stop passage of the budget Tuesday, she said it would not cooperate in passing any other bills before the session ends on May 10 in a threat to the government's pro-market reform agenda.

Parliament has been virtually paralysed for the government's second term in office by uproar over corruption scandals.

Singh's administration is still reeling from 2010 charges by the auditor that cut-rate allocation of telecom spectrum may have cost the exchequer $31 billion. Some 19 people, including a former minister, face trial over that scandal.