India's Central Bureau of Investigation (CBI) has said it is looking into whether a prosecutor for the agency discussed a probe into alleged corruption in the allocation of mobile phone airwaves five years ago with one of the people being investigated.

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Shares in Unitech Ltd fell more than 20 percent after reports on CNN-IBN TV and in the Times of India that CBI senior prosecutor AK Singh is suspected to have discussed the case with Unitech managing director Sanjay Chandra in a recorded conversation, reports Unitech strongly denied.

CBI spokeswoman Dharini Mishra announced on Tuesday that Singh was under internal investigation after the agency received a compact disc from an anonymous source on February 6.

She said the CBI was investigating the authenticity of the recording.

Unitech is a real estate developer that had a mobile phone joint venture with Norway's Telenor that was among those whose licences were revoked by a court following the high profile licensing scandal.

Telenor is in the process of dissolving the joint venture.

The two media reports said the recording was suspected to be of Singh coaching Chandra about how to deal with CBI investigators probing irregularities in the allocation of 2G airwaves.

Unitech issued a statement calling the recording fabricated.

"He [Chandra] wishes to make it absolutely clear that he has never met the prosecutor in the 2G case outside of Court or had any phone conversation with him," Unitech said.

Source: Agencies