Health authorities say the fight against malaria has saved 3.3 million lives worldwide since 2000 but the mosquito-borne disease still killed 627,000 people last year, mainly children in Africa. A shortage of funding and basic remedies like bed nets mean that malaria is still a major threat, particularly in Africa and southeast Asia, according to the World Health Organization's Malaria Report 2013.
"The fact that so many people are infected and dying from mosquito bites is one of the greatest tragedies of the 21st century," said WHO Director-General Margaret Chan.
A surge in global funding over the past decade has led to great strides against malaria, but even levels as high as $2.5 billion in 2012 are still only half what is needed to make sure everyone at risk of malaria has access to interventions, the WHO report said.
"This remarkable progress is no cause for complacency: absolute numbers of malaria cases and deaths are not going down as fast as they could," Chan said.
In 2012, there were an estimated 207 million cases of malaria, causing some 627,000 deaths.
The Democratic Republic of Congo and Nigeria are the hardest-hit among about 10 countries where malaria is a leading killer.
Tangible progress has been recorded in over half of the 103 countries with ongoing malaria transmission, with decreases in the incidence rate since 2000, said the WHO report.
Death rates worldwide fell by 45 percent between 2000 and 2012 in all age groups, and by 51 percent in children under five.
The main interventions for malaria are indoor spraying, diagnostic testing, artemisinin-based combination drug therapies, and bed nets treated with insecticides.
Malaria parasites are showing signs of resistance to insecticides in 64 countries.
Another main concern in the emerging resistance to the anti-malarial medicines' core component artemisinin in Thailand, Vietnam, Myanmar and Cambodia, the WHO report said.
But despite WHO recommendations that pills containing artemisinin only be removed from the market in favor of combination therapies to better protect against emerging resistance, nine countries -- six of them in Africa -- continue to make these drugs available.
Overall, access to combination drug therapies rose, with 331 million courses delivered in 2012, up from 76 million in 2006.
The report also raised concern about "a slowdown in the expansion of interventions to control mosquitoes for the second successive year," particularly regarding the distribution of bed nets.
"We went from a peak of more than 150 million nets distributed in 2010 to much lower numbers in 2011 and 2012," said Robert Newman, head of the WHO's Global Malaria Program.
In 2004, just six million insecticide-treated nets were delivered annually by manufacturers to malaria-endemic countries in sub-Saharan Africa.
Just 92 million of the 150 million needed annually were delivered by manufacturers in 2011, and only 70 million were delivered in 2012.
"In 2013 we have seen a strong upsurge... but that has not made up for the couple of years when we did not get enough bed nets out there," said Newman.
"We know that these are lifesaving tools," he said, noting that it costs about $12 for a net that can last three years.
"We can't wind up being victims of our own success," said Newman.
"If we don't finish the job, if we don't eliminate malaria in a country, then we know that we can undo in a couple transmission seasons what 13 years of hard work has achieved."