WASHINGTON (Reuters) - President Barack Obama on Monday announced a boost to funding for research into HIV/AIDS prevention and pledged up to $5 billion to support an international effort aimed at combating HIV/AIDS.

Speaking at the White House to mark World AIDS Day, the president said the United States would contribute $1 for every $2 pledged by other donors over the next three years to support The Global Fund, an international financing institution that fights AIDS, tuberculosis and malaria.

Obama also said he would redirect $100 million into a National Institutes of Health program to research a cure for HIV, the human immunodeficiency virus that causes AIDS.

"The United States should be at the forefront of new discoveries into how to put HIV into long-term remission without requiring lifelong therapies - or, better yet, eliminate it completely," Obama said at an event attended by Secretary of State John Kerry and software magnate Bill Gates, whose foundation has pledged up to $500 million for The Global Fund.

Obama also signed into law legislation authorizing an extension of a successful and popular program to combat AIDS worldwide, the President's Emergency Plan for AIDS Relief, known as PEPFAR.

PEPFAR funding has fallen 12 percent since 2010. Critics have accused Obama, a Democrat, of failing to show the same level of commitment to fighting AIDS as his Republican predecessor, Bush, who poured $15 billion into the program to combat AIDS worldwide.

Obama has argued that his administration has expanded the program's scope without increasing spending.

Globally, the United States is the largest donor to HIV efforts to fight HIV/AIDS in low and middle income countries, according to a report by the United Nations and the Kaiser Family Foundation. Overall donor government funding for HIV has remained at the about the same level since 2008, reflecting tighter budgets following the 2007-2009 financial crisis.

(Reporting By Mark Felsenthal; Editing by Cynthia Osterman)