Childhood deaths have declined across the world, data released on Thursday showed, but mortality is increasingly concentrated in poor countries.

A study by the United Nation's children's fund (UNICEF) showed that thanks to better prevention methods for malaria and action to reduce mother-to-child AIDS virus transmission, some 8.8 million children under five died in 2008 compared with 12.5 million in 1990.

But 99 percent of child deaths occurred in poor countries.

The United Nations millennium development goal 4 (MDG 4) calls for a two-thirds reduction in the mortality rate among children under the age of five years between 1990 and 2015.

To be on track to meet that figure, child mortality rate would need to reach 4.4 percent average annual rate of reduction, way above the 1.8 percent achieved so far.

The rate of decline in under-5 mortality is still grossly insufficient to obtain the MDG goal by 2015 particularly in sub-Saharan Africa and South Asia, said Danzhen You at UNICEF in New York in a commentary in The Lancet medical journal.

It is alarming that among the 67 countries with high mortality rates (40 per 1,000 or more), only 10 are on track to meet MDG 4. These findings call for a more concerted effort to accelerate progress, You and fellow authors wrote.

Sub-Saharan Africa now accounts for half of the 8.8 million under-5 deaths worldwide in 2008, while South Asia has the next highest rate of mortality in children with 32 percent.

The authors said, however, that since the data generally reflected mortality over the preceding three to five years, some major improvements including vaccination programs, work to combat the AIDS virus and more insecticide-treated mosquito net for malaria might not be fully reflected in the numbers.

There is evidence therefore to believe that the acceleration in child survival might already be well under way, the UNICEF commentators wrote.

There was urgent need, they added, for the global health community to refocus on pneumonia and diarrhea as two of the three most important causes of under-five mortality.

New tools, such as vaccines against pneumococcal pneumonia and rotaviral diarrhea, might provide much needed momentum and an entry point for the revitalization of comprehensive programing against these two diseases.