NEW DELHI (AFP) - India's scandal-hit government promised in court on Wednesday to reform the country's top police agency to give it greater independence as it carries out politically sensitive corruption investigations.

The Central Bureau of Investigation (CBI), nominally independent but long suspected of being under government influence, was rebuked by the Supreme Court earlier this year which called it a "caged parrot".

CBI investigators probing alleged graft in the government allocation of coal mining licences admitted sharing a report on the case with officials in the law and prime minister's offices before it was presented in court.

The CBI has undertaken several high-profile graft investigations in the second term of the government, including into the coal scandal, the 2010 Delhi Commonwealth Games and the allocation of telecom licences.

An affidavit approved by the cabinet and filed in the Supreme Court on Wednesday said the government would amend the 1946 Delhi Special Police Establishment Act, which created the CBI.

It promised to set up a three-member "Accountability Commission" of retired judges to investigate complaints and said a senior bureaucrat would monitor CBI-led trials to prevent meddling.

The government "shall not interfere with investigation or disposal of cases", it said.

Changes were also proposed to bolster the independence of the CBI chief, who would be appointed by a three-member panel comprising the prime minister, the Supreme Court chief justice and the leader of the opposition in parliament.

Only the national president would be able to sack him.

The CBI, whose report on the coal block scandal is still to be made public, has been probing charges by the national auditor last August that the government may have given away US$33 billion (S$42 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.

The CBI has also been accused in the past of going slow in probing charges of corruption against high-profile political figures, resulting in either their acquittal or non-prosecution.