Reliance Communications, India's second-largest mobile phone group, told the Supreme Court on Monday that it had been asked to tap 151,000 phones in a five year period from 2006 to 2010.

The figure, which will add to growing concern about the abuse of phone-tapping in India, was revealed during a hearing into a complaint by senior politician Amar Singh over the interception of his conversations.

"The government has to confirm that tapping is being done on consideration of security and also state how many phones are being tapped," opposition leader Arun Jaitley told reporters in Kolkata, the Press Trust of India reported.

"It is a cause of grave concern... the country's law states that tapping can be done in extreme cases like security considerations or in case of a serious crime."

Based on the Reliance figure, the Times of India estimated that up to 100,000 phones could be tapped every year in India.

Transcripts of tapped phone conversations have recently been reported by the Indian media, causing serious embarrassment to corporate titan Ratan Tata and senior journalists found cosying up to politicians.

In May last year, Outlook magazine claimed that government figures had ordered illegal taps on the phones of senior politicians, which caused uproar in parliament despite denials from the home minister.

Under Indian law, a phone can be tapped by half a dozen law enforcement agencies, but only on the grounds that there is an emergency or the tapping is in the public interest.