Mumbai: Say this about Anil Ambani: he does not take adversity lying down. The embattled Indian billionaire, questioned on Wednesday by the CBI probing a huge telecoms fraud, has been on the offensive since last week, when his group blamed 'baseless and motivated rumours' spread by rivals for a sharp selldown in his stocks.

Fit at 51 and married to a former Bollywood actress, the man who ranked 36th on last year's Forbes global rich list has never been shy about attacking his adversaries, most famously in a long-running feud with his older and richer brother, Mukesh.

Ambani is the highest-profile executive to be questioned in a widening corruption investigation that has led to arrests - including the telecom's minister - rocked Prime Minister Manmohan Singh's government, and cast a harsh light on the overlap of business and politics in booming India.

The dedicated marathon runner deftly avoided reporters as he left the Central Bureau of Investigation headquarters in New Delhi and was driven away in a white Ambassador car.

Ambani, who has an MBA from the University of Pennsylvania's Wharton School and whose empire includes No. 2 cellular carrier Reliance Communications (RCOM), has not been charged.

On Sunday, RCOM accused their telecoms rivals of "the brazen hijacking" of the 2G spectrum (airwaves).

"It is unfortunate that a malicious campaign of disinformation, falsehoods and calumny is being spread by RCOM's telecom industry competitors and corporate rivals, to put up a smokescreen and cover their own unprecedented irregularities," said Syed Safawi, CEO of RCOM's wireless unit.

One of those rivals, Bharti Airtel Chairman Sunil Mittal, told the Business Standard newspaper in an interview this week telecom operators "should shut their mouths" and let investigators do their job.

The latest sniping came days after stock in Reliance ADA, Anil Ambani's conglomerate, lost $2.5 billion in value in a single late-session plunge. The group called on regulators to investigate a 'vicious and illegal bear hammering of our listed stocks', following a selloff that helped make group flagship RCOM the worst performer this year in India's main Sensex index.

RCOM's shares are 88 per cent below their early 2008 peak and hit an all-time low last week. Its profit has declined for six straight quarters, and it had net debt of $7 billion in December, versus a market value of $4.5 billion.

"I think he is an ideal target for any slander campaign because his company is weak, it's leveraged and the reputation has been tarnished," said Eric Mookherjee, a Paris-based fund manager with Shanti India.

"Anil is a less powerful man than he was -- at least that's the impression I have," he said.

BROTHER'S SHADOW

The government may have lost $39 billion in revenue when the telecoms ministry gave out lucrative 2G licences and airwave frequencies in 2007/08 at below market prices, the state auditor has said.

An increasingly assertive Supreme Court has told federal police to go after more businessmen and politicians.

"You must catch all of them. Merely because a person is in the Forbes list of millionaires and billionaires does not matter," a Supreme Court justice was quoted as saying.

Although Anil is the more outgoing of the two, he has long been in the shadow of his older brother Mukesh, who ranks 4th on the Forbes global rich list and controls conglomerate Reliance Industries, India's most valuable listed company.

Belying his more staid image, Mukesh late last year moved his five-member family - and scores of servants - into a $1 billion, 27-storey home, featuring three rooftop helipads, that towers over south Mumbai.

Before they fell out, it was Anil who would make corporate presentations and take questions from reporters, whose names he made a point of remembering.

A member of the prosperous Gujarati community, Anil Ambani often speaks in the regional language to shareholders and business associates. He is a vegetarian, does not drink or smoke, and can often be seen among the early morning runners in Mumbai.

Once a fixture of Mumbai night life, he was linked with several starlets before marrying his wife some 20 years ago, and is a close friend of Bollywood superstar Amitabh Bachchan.

His taste for glamour is reflected in his business line-up, which includes theatre chain and production firm Reliance MediaWorks, and Reliance Broadcast Network Ltd, which has a 50-50 tie up with a unit of U.S. network CBS Corp for TV channels in India.

He is also no stranger to the corridors of power. He makes a weekly visit to the Indian capital and was elected as an independent member of Parliament in June 2004, with backing from the leftist Samajwadi Party. He resigned in March 2006, as did Congress party leader Sonia Gandhi, in a controversy over MP's holding profit-making positions, citing the need to uphold propriety in public life.

The Ambani brothers famously split after their father Dhirubhai's death in 2002 sparked a feud that led to a division of the family business empire in 2005. Mukesh got energy-based conglomerate Reliance Industries, the crown jewel, while Anil got Reliance Comm and the infrastructure and power businesses.

Dhirubhai Ambani was himself a legendary figure who rose from an impoverished village in Gujarat to found Reliance, a company that at one point accounted for 15 percent of India's exports.

The brothers' dispute came to a head over terms of a gas contract, which raged on even as they lived under the same roof with their mother and families, captivating India in a real-life soap opera.

In 2009, Anil attacked his brother and the oil minister in a series of newspaper ads, accusing the petroleum ministry of siding with publicity shy Mukesh.

The Supreme Court ultimately intervened and decided in Mukesh's favour. The 2010 ruling brought the brothers back to the negotiating table, where they unexpectedly agreed to scrap the non-competition pact that had been a source of conflict.

That prompted speculation, still unfulfilled, that they will work together again.

TRIPPED UP

Brotherly peace has not brought an end to Anil Ambani's woes.

Last month, he and two of his companies settled with market regulators over allegations of misuse of funds by misrepresenting the nature of investments and their profits and losses. Anil Ambani cannot invest in listed stocks until December.

Two days later and hours after running a half-marathon, he called a news conference, blasting coverage of the matter. His companies are known for their media battles.

In December, the Reliance Group issued a statement saying Anil was building "a multi-storey" residential complex in the posh Pali Hill section of Mumbai to house senior executives -- but not Anil himself. This came after media reports said Anil was building a tower almost as tall as his brother's in a project opposed by neighbourhood residents over its height.

Anil's attempts to put together deals that would pare RCOM's debt have come to naught. He was unable last year to find a buyer to take a 26 per cent stake in the company.

Plans to list RCOM's tower arm have not come to fruition either, while a deal that would merge the tower business with a rival's collapsed unexpectedly in September.

Since the sacking of the former telecoms minister in November, the main share index is down 9 per cent, while Reliance Comm has lost 41 per cent.

"It is a challenging time for him," said K.K. Mital, head of portfolio management services at Globe Capital in New Dehli. "The group needs good luck. But, unfortunately, it does not seem to be coming its way," he said.