US President Barack Obama sought Wednesday to rally the world's top and emerging powers to help cope with a global economic downturn, saying, "We can only meet this challenge together."

He also disputed criticism that the United States was feuding with other nations about the need to pump more money into economic stimulus policies, saying any differences are "vastly overstated."

"I am absolutely confident that this meeting will reflect enormous consensus about the need to work in concert to deal with these problems," Obama said before the G-20 economic crisis summit.

Obama prodded nations to spur growth and work together on regulatory reform, and not to fall into the kind of protectionism and other mistakes that helped fuel the Great Depression.

"That is a mistake that we cannot afford to repeat," Obama said alongside British Prime Minister Gordon Brown.

Obama called the world's economic challenge the most serious one since World War II. He said he came on behalf of the United States to "listen, not to lecture."

"Having said that," Obama added, "we must not miss an opportunity to lead."

Brown said that the extent of international cooperation was unprecedented, and that an economic plan was just hours away from being agreed.

Asked about whether the US was to blame for causing the economic slide, Obama said he preferred to look ahead, not back. He said he had no worries about the stability of the US economic system.

"I think that there is a vibrancy to our economic model, a durability to our political model, and a set of ideals that has sustained even through the most difficult times," Obama said.

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