Malaria killed nearly one million people worldwide in 2006, but better drugs and more mosquito nets in Africa are helping to thwart the tropical disease, the World Health Organization said in a report Thursday.

There were an estimated 247 million cases of malaria in the world in 2006, the most recent year that figures were available. Previously, the estimate was 350 million to 500 million cases.

"The change is due primarily to a refinement of calculation methods. It is not known if cases and deaths actually declined between 2004 and 2006," the WHO said in a statement.

"The reduction is primarily due to changes in the method for estimating the number of cases outside Africa. The method for Africa remained the same," the report said.

"The global burden of malaria remains enormous."

More progress has been made since the data were collected, said WHO Director-General Margaret Chan.

"I am personally confident that we will have even better news next year," Chan told reporters. "Right now, the momentum continues to build."

In 2005, the WHO set the goal of 80 per cent coverage in Africa for mosquito nets, drugs, indoor insecticide spray and treatment during pregnancy. Most countries are far from meeting the target.

For the first time, three African countries — Eritrea, Rwanda and Sao Tome and Principe —reported reductions in malaria deaths by 50 per cent or more, thanks to the four measures listed above and advances in disease surveillance.

In the 18 African countries surveyed in 2006, the percentage of children protected by insecticide-treated nets increased almost eightfold, from 3 per cent in 2001 to 23 per cent in 2006.

Malaria is a main cause of child mortality, said Ann Veneman, executive director for the United Nations Children's Fund.

"If the availability of bed nets and other key interventions can be increased, lives can be saved," she said.