Authorities are investigating top mobile phone carrier Bharti Airtel under provisions of the country's money launderingand foreign exchange rules, a minister said, sending its shares down as much as 5.1 per cent.

The Directorate of Enforcement is investigating cases against Bharti, junior finance minister S.S. Palanimanickam told parliament on Tuesday, but declined to give further details. 

"It may not be in the interest of the ongoing investigations to provide any further details," he said in a written reply to questions from a lawmaker. 

Bharti, controlled by billionaire Sunil Mittal, said it was cooperating with investigators. 

"We have already provided all relevant details asked for by the relevant authorities in this matter and will be happy to cooperate further, should the need arise," it said in a statement. 

Bharti, nearly a third owned by Southeast Asia's top phone company, SingTel, operates in 20 countries across Asia and Africa and is the world's fifth-biggest mobile phone carrier by subscribers. India is its biggest market. 

India's once-booming telecoms sector has been battered by a massive scandal over the below-market-price grant of lucrative telecoms licences in 2008, mostly involving smaller carriers. 

But market leaders Bharti and Vodafone's local unit are also being probed by police over "possible irregularities" in grant of airwaves to them in 2001 and 2002. Police conducted searches at Bharti and Vodafone offices in November in the case. 

By 0850 GMT, shares in Bharti, valued at more than $21 billion, were down 1.8 per cent at 302.40 rupees in a Mumbai market that was up 0.4 per cent. The shares had fallen to and intra-day low of 292.05 rupees before paring losses. (Times of India)