MUMBAI: The chief executive of Indian conglomerate Essar was interviewed by the Central Bureau of Investigation (CBI) Thursday as part of an investigation into a suspected multi-billion-dollar telecom fraud.

"He (Prashant Ruia) was at the CBI headquarters in relation to the spectrum probe," a company source told AFP, on condition of anonymity.

Ruia is one of several high profile Indian business tycoons to be quizzed by investigators in connection with the inquiry, among them billionaire Anil Ambani and Sanjay Chandra, managing director of property developer Unitech.

The Mumbai-based steel-to-shipping Essar group, with revenues of $15 billion, holds 33 percent of Vodafone Group's Indian unit, Vodafone Essar.

Essar issued a statement late Thursday which said that it "is in full compliance with DoT license norms and all other applicable laws."

"As and when any information is sought Essar will provide the same to the authorities," the statement said.

An Essar spokesman declined to give further details.

On Wednesday, Anil Ambani met CBI officials to answer questions over the second-generation (2G) licensing scandal in which the government sold mobile licences at knockdown prices in 2008.

The national auditor said late last year that irregularities in awarding the sought-after licences cost the exchequer up to $40 billion in lost revenues.

The CBI is looking into companies which may have benefited from suspected rigging of licence bidding rules under then telecom minister A. Raja and whether kickbacks were paid.

Raja was arrested with two former aides earlier this month in the scandal, as was a senior executive of one of India's biggest real estate firms DB Realty, which has a joint telecom venture with Abu Dhabi's Etisalat.

All the individuals and companies being probed have denied any wrongdoing.