TOKYO — The U.N. climate chief praised President Barack Obama's pledge to tackle global warming and expressed hope Friday that the U.S. policy shift would boost chances for a new international agreement on cutting emissions of greenhouse gases.

"It's been a night-to-day change in terms of the U.S. position on this topic," United Nations climate chief Yvo de Boer said in Tokyo, adding that he hopes that the more active American approach will encourage China and other developing nations to make further efforts to control their emissions.

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De Boer also said an Asian tour next week by U.S. Secretary of State Hillary Rodham Clinton, including stops in Japan, China, South Korea and Indonesia, would have "incredible importance" for global efforts on climate change.

He said South Korea is expected to become the first country to set an emissions reduction target out of the countries that did not set targets under the 1997 Kyoto Protocol, while Indonesia plays a key role because of deforestation, a growing problem in global warming.