WASHINGTON (Reuters) - President Barack Obama vowed to boost U.S. efforts to fight AIDS with a new target of providing treatment to 6 million people worldwide by 2013, up from an earlier goal of 4 million.

At a celebrity-studded World AIDS Day event on Thursday, Obama also challenged other nations to boost their commitments to fund treatment and called on China to step up as a major donor in the effort to expand access to AIDS drugs.

We can beat this disease. We can win this fight. We just have to keep at it, today, tomorrow, and every day until we get to zero, Obama said at the forum, where he credited his Republican predecessor, George W. Bush, for his efforts to combat AIDS and HIV.

As we go forward, we need to keep refining our strategy so that we're saving as many lives as possible. We need to listen when the scientific community focuses on prevention, Obama said.

Bush, who sought to make the fight against AIDS and HIV a signature issue of his presidency, spoke by satellite to the Washington event sponsored by the ONE campaign, an organization dedicated to fighting poverty and preventable disease.

Advocacy groups welcomed the new treatment target from the United States, the largest global AIDS donor by country, at a time when they are reeling from a funding crunch. Annual funding for HIV and AIDS programs fell to $15 billion last year, well below the $22 billion to $24 billion United Nations agencies say is needed by 2015.

We hope this marks the end of donors walking away from supporting global HIV/AIDS, despite evidence that the epidemic can be reversed. Dr. Tido von Schoen-Angerer of medical charity Medecins Sans Frontieres said in a statement.

MINORITY GET TREATED

New HIV infections fell to 2.7 million in 2010, down from 3.1 million in 2001, while the total number of people getting life-saving AIDS drugs rose to 6.65 million in 2010 from just 400,000 in 2003, according to recent data.

But that is still a minority of the 34 million people around the world who had the human immunodeficiency virus in 2010. Studies have also shown that suppressing the virus through treatment reduces HIV's spread to patients' partners by as much as 96 percent.

As part of a goal to achieve an AIDS-free generation, Obama said the United States aimed to provide anti-retroviral drugs to more than 1.5 million HIV-positive pregnant women worldwide by 2013.

He announced a $50 million increase in spending on HIV and AIDS treatment in the United States, where only 28 percent of the 1.2 million Americans living with the infection have it under control, according to health officials.

The funds would come from existing resources and would not require congressional approval, a White House official said.

Main manufacturers of HIV drugs include Gilead Sciences Bristol-Myers Squibb and Abbott Laboratories.

The AIDS issue seemed to prompt a rare instance of bipartisan agreement at a time when Democrats and Republicans have been bitterly divided over tax policy and spending cuts.

Both Republicans and Democrats in Congress have consistently come together to fund this fight, Obama said. That's testament to the values that we share as Americans, a commitment that extends across party lines and that is demonstrated by President Bush and I joining you all today.

In his remarks via satellite from Tanzania, Bush said he understood that many nations, including the United States, were struggling with their budgets. But he said wealthy nations had an obligation to make the fight against AIDS a priority.

We're a blessed nation in the United States of America, and I believe we are required to support effective programs that save lives, Bush said.

(Additional reporting by Jeff Mason and Emily Stephenson; Editing by Michele Gershberg bad Cynthia Osterman)