The Central Bureau of Investigation (CBI) on Tuesday questioned a top executive of Unitech Ltd as part of a probe into a telecoms corruption scandal that has roiled politics and spooked investors in Asia's third-largest economy.

Unitech Managing Director Sanjay Chandra was at the CBI headquarters on Tuesday, answering questions over his role in a case that charges his firm was favoured by a former telecoms minister when mobile phone licences were issued in 2008, a police spokeswoman said.

In continuation of the ongoing investigations, I am here today to personally clarify certain issues raised by the CBI, Chandra said in a statement issued by his publicist.

Unitech has a mobile telecoms joint venture in India with Norway's Telenor.

Police have so far arrested Andimuthu Raja, the former telecoms minister, and a senior official of Etisalat's local unit, whose Indian partner is also accused of receiving favours.

They have also questioned officials from Reliance ADA group, which controls No 2 telecoms firm Reliance Communications.

All firms have denied wrongdoing.

Executives at Tata Teleservices, the fifth-ranked mobile carier and part of the Tata group, have also been questioned, a source familiar with the matter said.

The scandal, one of the many during the Congress-led government's second term, has distracted from policymaking, further delaying crucial economic reforms such as opening up the retail and financial sectors to foreign investors.

The government is close to caving in to a demand from the main opposition Bharatiya Janata Party to set up a cross-party probe into the case.