Indian federal police are investigating the role of top tycoon Anil Ambani in a multi-billion dollar telecoms scandal that has rocked its political and business elites, the Press Trust of India (PTI) news agency said on Thursday.

The 52-year-old billionaire is the highest-profile company executive to be drawn into the investigation of whether lucrative radio spectrum and mobile phone licences were sold at below-market prices in return for kickbacks.

The scandal is the biggest of several corruption cases to emerge in Prime Minister Manmohan Singh's second term. It has damaged the government's credibility and thrown into the spotlight the behaviour of leading industrialists and politicians.     

A lawyer for the Central Bureau of Investigation (CBI) told the Supreme Court that Ambani himself was now under investigation, after he was questioned earlier this year by police, according to PTI.

A CBI spokeswoman said she could not confirm the investigation of Ambani, who controls No. 2 mobile carrier Reliance Communications as part of his Reliance ADA conglomerate.

He denies wrongdoing in the telecoms case. A Reliance ADA spokesman declined to comment on Thursday.

Three of his executives are already in jail awaiting trial, accused of conspiring to set up a front company to gain valuable radio spectrum during the sale, which a state auditor said cost the government up to $39 billion in lost revenues.  - Reuters