MUMBAI (AFP) - Reliance Industries, India's biggest private firm, plans to invest 1.5 trillion rupees (S$33 billion) in its businesses over the next three years, chairman Mukesh Ambani told shareholders on Thursday.

"We will be embarking on this investment, the largest we have ever undertaken, in all our five businesses simultaneously," Mr Ambani said at the energy giant's annual general meeting in Mumbai.

Reliance, controlled by India's wealthiest man Ambani, has expanded into the fast-growing broadband and retail segments in recent years.

But analysts have grown concerned about the ability of Reliance, India's largest private oil explorer, to raise gas production from its blocks off the nation's east coast.

Mr Ambani did not reveal funding plans for the investments.

The company has built up a war chest for acquisitions, with cash reserves of more than 829 billion rupees as of the March-end quarter.

Mr Ambani's announcement comes at a time when India's economy has slowed sharply to a decade-low of 5 per cent in the fiscal year to March.

"New projects will come on stream when the global economy recovers," he said.

In 2011, British energy giant BP paid US$7.2 billion to acquire a 30 per cent stake in 21 of Reliance's oil and gas fields.