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UNITED NATIONS - The world's population will likely reach 9.2 billion in 2050, with virtually all new growth occurring in the developing world, a UN report said Tuesday.

According to the UN Population Division's 2006 estimate, the world's population will likely increase by 2.5 billion people over the next 43 years from the current 6.7 billion - a rise equivalent to the number of people in the world in 1950.

Hania Zlotnik, the division's director, said an important change in the new population estimate is a decrease in expected deaths from AIDS because of the rising use of anti-retroviral drugs and a downward revision of the prevalence of the disease in some countries.

The new report estimates 32 million fewer deaths from AIDS during the 2005-2020 period in the 62 most affected countries, compared with the previous UN estimate in 2004.

This change contributed to the slightly higher world population estimate of 9.2 billion in 2050 than the 9.1 billion figure in the 2004 estimate, the report said.

The report also said most population growth will take place in less developed countries, whose numbers are projected to rise from 5.4 billion in 2007 to 7.9 billion in 2050. The populations of poor countries like Afghanistan, Burundi, Congo, Guinea-Bissau, Liberia, Niger, East Timor and Uganda are projected to at least triple by mid-century.

By contrast, the total population of richer countries is expected to remain largely unchanged at 1.2 billion. The report said the figure would be lower without expected migration of people from poorer countries, averaging 2.3 million annually.

According to the report, 46 countries are expected to lose population by mid-century, including Germany, Italy, Japan, South Korea and most of the former Soviet republics.

Zlotnik said most countries in Asia and Latin America have reached the "relatively beneficial stage" of having more working-age adults than children or elderly in their populations, "and they will remain in that stage for at least two more decades."

But their populations will then start to age, heading in the same direction as Europe and North America, she said.

"Europe is the only region at this moment where the number of people aged 60 and over has already surpassed the number of children," she said. "We expect that Asia and Latin America will have by 2050 an age distribution that is very similar to the one that Europe has today."

African countries will have an increase of working-age adults by 2050, but the continent's overall population will also nearly double in that time, Zlotnik said.

"So it is the continent that is going to have to absorb a very high increase, and it will have to absorb it at levels of development that are the very lowest that we have in this world," she said.