Poverty and war are harming advances in infant mortality, particularly in sub-Saharan Africa, a new Unicef report on global child health has said.
Sub-Saharan Africa is at the bottom of the child survival table
Globally, 62 countries were making no or insufficient progress towards a key 2015 child mortality target, it said.
Sierra Leone was the worst performer, with 270 deaths before the age of five per 1,000 live births, in 2006 figures.
This compares to three deaths per 1,000 in the world's six best performers, which included Sweden and Singapore.
The attainment of the 2015 goal - called the fourth Millennium Development Goal (MDG), which requires a two-thirds reduction in the 1990 under-five mortality rate - "is still possible, but the challenge is formidable", the report says.
In its report, the State of the World's Children 2008, Unicef notes that over the long term there has been a significant improvement in child survival, with a 60% fall in child mortality rates since 1960.
For the first time since records began, it says, in 2006 the estimate of the absolute number of under-five deaths fell below 10m to 9.7m.
But the picture painted in the report is one of divergence, with the industrialised world and parts of the developing world making good progress.
The world's best performers were Sweden, Singapore, San Marino, Liechtenstein, Iceland and Andorra, with three infant deaths before the age of five per 1,000 live births.
But other parts of the developing world are left behind. This includes in particular sub-Saharan Africa, home to 28 of the 30 countries with the highest mortality rates.
Here, the annual average rate of reduction in the child mortality rate between 1990 and 2006 was only 1% per year - meaning the rate will have to increase to 10.5% per year between 2007 and 2015 if the region is to meet the fourth MDG.
In addition to sub-Saharan Africa, insufficient progress was recorded in the Middle East and North Africa (Mena) and South Asia.
But other developing countries have made good progress towards the target.
In East Asia and Pacific, and Latin America and the Caribbean, mortality rates almost halved to 27 deaths per 1,000 live births - leaving those regions on track to meet the goal.
In industrialised countries in general, there are six deaths per 1,000 births.
Nonetheless, the report laments, an average of more than 26,000 infants under five die every day around the world.
In Brazil, targeted action has produced results
They mostly die from preventable causes such as diarrhoea, malaria, malnutrition, mother-to-child transmission of HIV, unsafe water, poor hygiene and neonatal problems.
The solutions to child deaths are well-known, says the report - "simple, reliable and affordable interventions with the potential to save two-thirds of the children currently at risk are readily available".
"The key," said David Bull, executive director of Unicef UK, "is to expand the reach of proven health strategies to help save the lives of children in the poorest and most difficult-to-reach communities."
Such interventions that have already been shown to be effective include promoting breast-feeding, immunisation, vitamin A supplementation and the use of mosquito nets.
War and poverty
But obstacles include limited, disease-specific rather than integrated approaches to health care; the low profile of maternal and child health; intermittent financing and lack of political will.
In many cases, lack of progress may be attributed to poverty and war - as in the three worst performers, Sierra Leone, Angola and Afghanistan.
"Today we are calling for the global community to put child survival at the heart of the development agenda and make it a priority at this year's G8," said Mr Bull.
"Child survival must be a global imperative."