WASHINGTON (AFP) - US President Barack Obama on Monday pledged up to US$5 billion (S$6.3 billion) to fight HIV/Aids as long as the rest of the world collectively offers double that amount.

Mr Obama urged other countries to replenish the Global Fund to Fight Aids, Tuberculosis and Malaria as part of a White House event marking World Aids Day which fell on Sunday.

Mr Obama also announced a new plan to seek a cure for HIV, the virus that causes Aids, which will see US$100 million go towards the development of therapies at the National Institutes of Health.

"Don't leave our money on the table," Mr Obama said, calling for a new global effort to spur funding for Aids research.

"It's been inspiring to see the countries most affected by this disease vastly increase their own contributions to this fight - in some cases, providing more than donor countries do.

"That ought to inspire all of us to give more, to do more, so we can save more lives." The initiative will see Washington donate one dollar for every two dollars collectively offered by other nations up to a US total of US$5 billion over the next three years.

Mr Obama also announced that the US President's Emergency Plan for Aids relief (PEPFAR), a program started by his predecessor George W. Bush, had smashed through a target of treating six million people.

"I'm proud to announce that we've not only reached our goal, we've exceeded our treatment target. We've helped 6.7 million people receive lifesaving treatment," Mr Obama said.

Mr Obama also said that the United States planned next year to convene a conference with its global partners to set common goals for battling the disease.

The Foundation for Aids Research (amfAR) welcomed Mr Obama's announcements, including the US$100 million for the search for an HIV cure.

"We cannot achieve the President's goal of an AIDS-free generation without continued investment in the research necessary to ultimately help us find a cure for this disease," said Rowena Johnston, amfAR's vice president and director of research.

The Obama administration says it has improved and expanded on PEPFAR - which the president described as a "phenomenal" achievement of his predecessor George W. Bush.

The program has now reached 1.5 million pregnant women with HIV with antiretroviral drugs to prevent HIV transmission to their children.

It also marked a milestone in June with the birth of the one millionth infant born HIV-free because of PEPFAR's support.