Men accounted for three-quarters of all the deaths, a figure rising to 84 percent in the developing nations where 930 million of the world's 1.1 billion smokers are to be found.

The figures are based on work done by researchers from Harvard School of Public Health in Boston, Massachusetts and Australia's Queensland University, and published in the Lancet medical journal Friday.

The main causes of the tobacco-related deaths were heart and lung diseases, they noted.

The news comes as the major tobacco companies, increasingly under siege in the industrialized world, switch their sales efforts to emerging nations with their expanding populations and rising spending power.

"Our findings mark the beginning of an era when the majority of smoking-caused deaths occur in developing countries," lead author Majid Ezzati of Harvard said.

"Smoking-related deaths will rise substantially, especially in developing countries, unless effective intervention and policies to curb and reduce smoking among men and prevent rises among women are implemented," he added.

Ezzati said that although anti-smoking policies were being widely implemented in the developed world, they were lagging far behind in the poorer nations, which consequently faced a rising hazard.

The World Health Organization (WHO) estimates that tobacco-related deaths will at least double by 2030 as smoking takes its toll of men in the developing world and more women start to take up the habit.

"This should provide a motivation to strengthen the case to implement tobacco control programs and policies, which have generally lagged in developing countries, worldwide," Ezzati said.

Earlier this year the WHO adopted a sweeping anti-tobacco treaty in a bid to curb the product that it said is a death warrant for half its habitual users.