President Barack Obama hit back at claims the United States had stalled in Afghanistan and vowed foreign forces would not be needed "in perpetuity", in a rare Australian TV interview aired on Thursday.
Obama, speaking to public broadcaster ABC's 7.30 Report in Washington, also backed President Hamid Karzai, dismissing recent controversies.
"I would dispute the notion that it's not getting better. I do think that what we've seen is a blunting of the momentum of the Taliban which had been building up in the year prior to me taking office," Obama said.
"What I have said is that we need to begin drawing down our troops in 2011, and start handing over more and more responsibility to the Afghans," he added.
"We can't be there in perpetuity. Neither the American people nor the Australian people should be asked to carry that burden any longer than it needs to be carried."
Obama suggested Karzai, who came to power after the US-led invasion of 2001 ousted the Taliban, may have been misquoted in recent reports that said he had threatened to join the militants.
But he said Washington would continue to "put pressure" on Karzai to deliver reforms that would tackle corruption and improve the lives of ordinary Afghans.
"I think that President Karzai is capable of leading his country into the 21st century and stabilising it. He's got a tough task but the reason we're there ultimately is not to support one man," Obama said.
"We think it's necessary for the world's security that we dismantle Al-Qaeda and its affiliate networks, and we need a strong partner in that process," he added.
"I think Karzai has the capacity to be that strong partner and I think that we're going to have to... continue to put pressure on him to make the kinds of reforms and improvements that will not only mean success for us but also ultimately success for him."
Karzai also recently accused Western powers of trying to rig last year's presidential election, drawing an initially strong response from Washington. Obama paid a surprise visit to the Afghan leader last month.
In the wide-ranging interview, Obama also said China can't be allowed to wait before tackling climate change.
"Right now their understandable impulse is to say, 'Well, let's let the developed countries, the Australias, and the Americas deal with this problem first and we'll get to it when we've caught up a little bit in terms of our standard of living'," he told ABC.
"The point we've tried to make is we can't, we can't allow China to wait."
China has overtaken the United States as the biggest carbon polluter, but some participants accused it of vetoing attempts to forge a stronger agreement at December's UN climate talks in Copenhagen.
Obama added that the United States was not interested in "constraining" China as it rises to become a major world power, but urged Beijing to recognise its growing responsibilities.
Obama gave the interview after being forced to cancel last month's visit to Australia to push through landmark health reforms.
He said he was looking forward to visiting the country with his wife and daughters in June, and described Prime Minister Kevin Rudd as "smart but humble".
"Kevin is somebody who I probably share as much of a world view as any world leader out there," he said.