Indian Prime Minister Manmohan Singh, weakened by a corruption scandal involving his sacked telecoms minister, told the Supreme Court on Saturday he had done nothing wrong and had followed correct procedures.

In a rare move, the Supreme Court this week reprimanded Singh for failing to probe ex-telecoms minister Andimuthu Raja over allegations he had sold licences too cheaply. The court demanded Singh himself explain what had happened, tarnishing his squeaky-clean image.

While Singh and his coalition government are likely to survive the scandal, the criticism is expected to further weaken the federal government's ability to move key economic reforms through parliament.

On Saturday, an affidavit, seen by Reuters, was presented to the country's top court by Singh's representative, Attorney General G.E. Vahanvati. The document said the prime minister had done "all that was required in the interest of probity".

Corruption has long been a major problem in India, recognised by all political parties.

The ruling Congress party has pledged to crack down on graft, but it has been put on the defensive in recent weeks when it was forced to fire three senior officials over corruption allegations, including the problem-riddled Commonwealth Games.

India was ranked 87th in Transparency International's 2010 ranking of 178 nations based on the perceived level of corruption, or almost in the middle of the index. Rival China is ranked higher, at number 78.

Singh, a former finance minister who led the drive to open up India's economy in 1991, has long been criticised for being weak prime minister, contanstly trying to satisfy his coalition partners for the government to remain in power.

Much of the decision-making power also lies with Sonia Gandhi, the chief of the Congress party and Singh's powerful Finance Minister Pranab Mukherjee.

Senior members of the ruling Congress party have rallied around Singh, saying he has done nothing wrong and dismissed any rumours the prime minister was planning to resign.

"It is often said these are testing times. In fact I can not help feeling that we in India are living always through testing times. Indeed as prime minister I sometimes feel like a high school student going from one test to another," Singh told a leadership summit in New Delhi on Saturday.

In his first comments since the corruption scandal blew up, Singh said several investigating agencies were looking into the issue, which could potentially emerge as the country's biggest graft case. Singh said the guilty will not be spared.

"There should be no doubts in anybody's mind that if any wrong thing has been done by anybody, he or she will be brought to book," he said.

Parliament has been deadlocked for the past 10 days over opposition demands for a full investigation into the sale of the second-generation telecoms licences in the world's fastest growing mobile phone market.

Raja is accused of selling the licences too cheaply in 2007-2008, potentially costing the state up to $31 billion in lost revenues, according to an audit by an official watchdog. The process also violated several rules, the audit said.-Reuters