Indian tycoon Anil Ambani's Reliance ADA Group, which controls No. 2 mobile carrier Reliance Communications, said on Friday authorities had examined some of its officials and that it was cooperating.

The Central Bureau of Investigation (CBI) has been looking into possible irregularities in the allocation of telecommunications licences and radio airwaves after a state auditor said licences were sold too cheaply in 2007-08, at a cost to the government of up to $39 billion in potential revenue.

The telecoms licensing scandal is one of several that has tarnished the government of Prime Minister Manmohan Singh, led to a near-shutdown of parliament and rattled investors.

The Supreme Court had directed the CBI to probe licence grants starting from 2001.

The CBI is reportedly examining a large number of telecom companies and their officials over the past several weeks, in relation to various matters relating to the years 2001 to 2008, a group spokesperson said in a statement late on Friday.

As part of this process, CBI has also examined a few officials of Reliance ADA Group, and we are fully co-operating with the authorities in this regard, the statement said.

Reliance Communications, predominantly a CDMA carrier, was granted rights to expand its GSM services in 2007.

In a report released in November, a government auditor said Swan Telecom, which was later renamed Etisalat DB, was awarded a licence even though a unit of Reliance Communications held more than 10 percent of equity in the firm, a violation of rules.

Reliance Communications has said the group did not have any shareholding in Swan when licences were awarded in January 2008.

Reliance ADA Group firms including Reliance Communications this week saw their share prices fall sharply, which the group blamed on rivals for spreading what it said were baseless rumours.

Earlier on Friday, it said some stock brokers were spreading baseless sensational charges against it, without naming anyone.