Sixteen leaders including US President George W. Bush, Chinese President Hu Jintao and Indian Prime Minister Manmohan Singh met at a Japanese mountain resort for a first of its kind climate change summit.

But developing nations rejected as too weak a call made a day earlier by the G8 powers -- Britain, Canada, France, Germany, Italy, Japan, Russia and the United States -- for global emissions cuts of at least 50 percent by 2050.

The deadlock between rich and developing nations has held up talks on reaching a new climate treaty by the end of 2009 in Copenhagen -- a goal set in December at a UN-backed conference in Bali.

"Climate change is one of the great global challenges of our time," the leaders said in a statement. "Our nations will continue to work constructively together to promote the success of the Copenhagen climate change conference."

Bush, Hu and Japanese Prime Minister Yasuo Fukuda smiled and chatted with one another as they posed for a group photograph after the meeting here in the secluded hills of northern Japan.

But their statement said only that rich countries will implement their own goals for cutting greenhouse emissions while developing major economies would also take action, without proposing any numbers.

It did not include a Japanese proposal for developing nations to agree to long-term cuts in emissions in exchange for action in the nearer term by rich nations, one of the key sticking points in global climate change talks.

The Group of Eight powers on Tuesday called for the world to cut carbon emissions by at least 50 percent by 2050 and urged developing countries to reciprocate in kind.

But the so-called Group of Five -- Brazil, China, India, Mexico and South Africa -- immediately countered with a call for the rich nations to take the lead, saying they were historically responsible for climate change.

"I think this is just their tactics," said Japan's chief government spokesman Nobutaka Machimura. "I don't know on what basis they're speaking."

But Kim Carstensen, head of the WWF environmental group's Global Climate Initiative, accused rich nations of trying to stall action by blaming developing nations.

"Some rich nations get lost in tactics and seem to forget that the survival of people and nature crucially depends on their leadership," he said.

The developing bloc urged rich countries to cut emissions by 25 to 40 percent by 2020 from 1990 levels. The G8, in line with Bush's policy, said only that each G8 country would set its own target for the mid-term period after 2012, when the Kyoto Protocol's obligations to cut emissions expire.

The United States is the only major industrial country to reject the Kyoto Protocol, with Bush arguing that it is unfair by making no demands of fast-growing emerging economies.

But both major candidates to succeed Bush -- Barack Obama and John McCain -- have proposed tougher action on climate change, meaning that real decisions on gas emissions would almost certainly wait until after the November election.

French President Nicolas Sarkozy said that Tuesday's agreement meant the G8 "now has made a commitment" on cutting emissions but that emerging economies have not done the same.

"The United States is making a commitment, firmly and absolutely, with the condition imposed by their Congress that China and India also take action in a differentiated way," Sarkozy told reporters.

"No matter whether McCain or Obama wins the election in November, the American position will be more proactive, but that doesn't mean that they would be ready to give without reciprocity," he said.

Rich nations and rising economic powers were also using the meeting to discuss ways to rein in surging oil and food prices that are taking their toll on the global economy.

During talks between the G8, leaders of five emerging economies including Hu and Singh "expressed hope for further cooperation with the G8 on global issues, especially the food crisis," a Japanese foreign ministry official said.

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