The billionaire founder of the Virgin Group of companies made the announcement in New York at the second annual Clinton Global Initiative conference, held on the sidelines of the United Nations General Assembly.

The initiative, launched by former US president Bill Clinton, is aimed at tackling key global problems such as climate change, poverty and religious and ethnic tensions.

"We have to limit our dependence on fossil fuels," said Branson. "We hope that this contribution will help in some small way to enable our children to enjoy this beautiful world."

Branson said Virgin Group would invest all future profits from its airline and train businesses in renewable energy initiatives within and outside the company.

According to a Virgin Group statement, Branson and his company "believe that all businesses, especially those involved in transportation, energy, and particularly fossil fuels such as coal, must be at the forefront of developing environmentally-friendly business strategies with a focus on replacing traditional energy with energy coming from renewable sources."

To demonstrate that commitment, the company said that all "dividends, realizations and share sales" from Virgin's transportation interests "will be invested into renewable energy initiatives ... to tackle emissions related to global warming." That commitment was estimated at three billion dollars over the next 10 years.

Branson told the BBC in an interview his pledge had been solicited by Al Gore, who served as Clinton's vice president and is spearheading efforts to fight global warming.

Clinton applauded Branson's generosity and commitment to the cause.

"Richard's commitment is groundbreaking not only because of the price tag -- which is phenomenal -- but also because of the statement that he is making: Clean energy is good for the world, and it's good for business," the former US president said in a statement.

In an interview with the Fox television network, Branson outlined his strategy.

"Basically, what we are saying is that any monies that the Virgin Group makes from our transportation business, which we'll put into developing new fuels, building ethanol plants, and hopefully, if we can come up with the right kind of new fuel, hopefully we can actually make some money out of it, which we can reinvest in more fuels."

Asked in the BBC interview about the marketing advantage of the move, the flamboyant entrepreneur known for outlandish marketing schemes said: "If it's good for marketing, that's fine, but it's not my principal reason for doing it."

Branson, whose Virgin brand labels a variety of business, including Virgin Atlantic Airways and entertainment retailer Virgin Megastores, pledged the largest amount at Thursday's conference, raising the total commitment to 5.7 billion dollars.

At the first conference last year, less than half that was pledged, 2.5 billion dollars.

The Virgin Group said its initiative would take the form of investment in new fuel technologies through a unit called Virgin Fuels, for which Branson's group has pledged 400 million dollars in the next three years.

The first investment project of Virgin Fuels will be in a California-based ethanol company called Cilion. Further investments over the next three years will be made in Europe and other parts of the world, the company said.

Branson recently was ranked by Forbes magazine as the 245th richest person in the world, with a net worth of 2.8 billion dollars.

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