Malaria deaths have dropped dramatically since 2000, the World Health Organization (WHO) has said.

It said cases are falling steadily, thanks to more people being diagnosed and treated, and more people getting bed nets.

Yet progress against the mosquito-borne infection remains fragile.

West African countries suffering an unprecedented epidemic of Ebola are particularly at risk of seeing a resurgence of malaria, the United Nations health agency said.

In its annual report on the disease, the WHO said the malaria death rate fell by 47% worldwide between 2000 and 2013 and by 54% in Africa, where about 90% of all malaria deaths occur.

In an analysis of malaria's impact across sub-Saharan Africa, it also found that despite a 43% increase in population, fewer people in the region are infected every year.

"The next few years are going to be critical to show that we can maintain momentum and build on the gains," said Pedro Alonso, director of the WHO's global malaria programme.

In west Africa, according to the report, the deadly Ebola outbreak has had a "devastating impact" on malaria treatment and the roll-out of malaria control programmes.

In Guinea, Sierra Leone and Liberia, which have all been severely hit by the Ebola epidemic, many inpatient clinics are closed and attendance at outpatient facilities is a fraction of rates seen before the outbreak, it said.

With a major malaria threat in these countries, which together saw about 6.6 million cases and 20,000 malaria deaths in 2013, the WHO called for temporary control measures.

It wants malaria drugs given to all patients with fever and called for mass treatment to be carried out in areas hard hit by both Ebola and malaria.

"International donor financing is being stepped up to meet the further recommendation that bed nets be distributed to all (Ebola) affected areas," the report said.

Worldwide, malaria killed about 584,000 people in 2013, including about 453,000 children under five years old.

Although funding to fight malaria has increased threefold since 2005, it is still only around half the $5.1 billion needed (€4.15bn).

WHO director general Margaret Chan said the data showed the fight against malaria could be won, because "we have the right tools and our defences are working".

"But we still need to get those tools to a lot more people if we are to make these gains sustainable."