Rwanda is among the countries which have succeeded in substantially accelerating their rates of reduction in child mortality during the last decade, the United Nations said Thursday.

The number of infants and children who die before reaching the age of five has dropped from 12 million in 1990 to 6.9 million in 2011, according to the UN Children's Fund, UNICEF.

The UNICEF report, titled "Committing to Child Survival: A Promise Renewed," says under-five deaths are now increasingly concentrated in sub-Saharan Africa and South Asia, which now account for 80 percent of the world total.

"Other countries such as Cambodia, Zimbabwe and Senegal have succeeded in substantially accelerating their rates of reduction in mortality during the last decade," says the report. Rwanda's 2011 estimate is 54 per 1,000 live births.