Progress in cutting the number of deaths among children under five is still "grossly insufficient" in some parts of the world, Unicef has warned.
Its report, published in the Lancet, shows there has been a fall of 28% in child deaths since 1990.
But the UN children's agency warns many poorer countries will not meet the 2015 Millennium Development Goal of cutting that figure by two thirds.
The situation is worst in sub-Saharan Africa and south Asia, it said.
Last year, 9.2m children aged under five died across the world.
Central and eastern Europe, Latin America and the Caribbean and East Asia and the Pacific countries have cut deaths among under-fives by over 50% since 1990.
But over the same period, deaths in western and central Africa have fallen by just 18%; in sub-Saharan Africa the figure was 21%, while in eastern and southern Africa it was 26%.
In Sierra Leone, the country with the worst under-five mortality rate in the world, 262 out of every 1,000 children die before their fifth birthday.
The rate for industrialised nations is just six deaths per 1,000 live births.
However Unicef says there are developing countries, such as Haiti, Eritrea and Turkmenistan, where major progress has been made.
Its report is published to mark the 30th anniversary of the Alma-Ata declaration which highlighted the issue of child deaths.
It warns that malnutrition is now a contributing cause in around a third of deaths
HIV and Aids have had a significant impact on child deaths, and parental deaths and illness have made collecting accurate figures difficult.
But Unicef says better HIV prevention is likely to help improve child survival.
It cites countries such as Botswana, Lesotho and Swaziland where deaths from HIV/Aids among under fives are beginning to decline.
The Unicef report says that while interventions in some areas, such as immunisations or insecticide-treated bednets to prevent malaria, have been effective, there is a “disappointingly" low coverage of services to treat pneumonia and diarrhoea.
Writing in the Lancet, the researchers said: "Substantial progress has been made.
"But progress is still grossly insufficient, particularly in much of sub-Saharan Africa and south Asia."
They said working to improve sanitation, nutrition and HIV prevention, as well as better data collection, in these areas was key.
Unicef executive director Ann Veneman said: "Since 1960, the global under-five mortality rate has declined more than 60%, and the new data shows that downward trend continues."
She added: "There are also encouraging improvements in many of the basic health interventions, such as early and exclusive breast-feeding, measles immunisation, Vitamin A supplementation, the use of insecticide-treated nets to prevent malaria, and prevention and treatment of HIV/Aids.