US computer billionaire Bill Gates has doubled the funding he gives to a body set up to fight disease in the developing world.
Bill Gates has called for more effort to be made on reducing health inequality
He told the annual assembly of the World Health Organization more needed to be done to fight health inequality.
The Microsoft founder pledged an extra $250m to Grand Challenges in Global Health, which he set up in 2003.
The assembly is due to debate plans to tackle malaria, polio and influenza.
Speaking on the first day of the assembly, which lasts until May 25, Mr Gates said: "There is a tragic inequity between the health of people in the developed world and the health of those in the rest of the world."
Mr Gates, who has given billions to various health campaigns, added "I am an optimist. We have a historic chance to build a world where all people, no matter where they're born, can have preventative care, vaccines and treatments they need to live a healthy life."
He said to achieve that goal there needed to be greater political leadership and more research into diseases which affect the developing world, including incentives for private firms.
And he added he hoped the extra money for the Grand Challenges initiative, which supports research into diseases that disproportionately affect the developing world, would help redress some of the imbalance.
The speech kick-started the assembly, which is the WHO's supreme decision-making body and brings together all 192 member countries.
On the agenda is a review of worldwide controls to guard against global epidemics such as influenza.
Many health officials believe countries are unprepared for a major flu pandemic.
Part of the problem is that the WHO's international health regulations were last updated in 1981 and effectively only allow global controls such as travel restrictions and surveillance to be introduced in the event of cholera, plague and yellow fever outbreaks.
But the reform could be hampered over fears about the economic impact restrictions can have.
Denis Aitken, a senior aide to the WHO's director general Lee Jong Wook, said there was still some negotiating to be done.
But he added: "Most states are reasonably optimistic."
African states, where 89% of the 1m-a-year victims of malaria live, were also expected to ask the assembly to reinforce its action against the mosquito-borne disease by increasing funding.
And the WHO's attempts to eradicate polio by the end of this year are also set to be criticised.
The target is almost certain to be missed as mass immunisation programmes have so far failed to stop the spread of the crippling and potentially deadly disease.