Secretary-General Ban Ki-moon said Wednesday that China's leaders have assured him they want to seal a deal on a new U.N. climate treaty at a conference in Copenhagen, Denmark in December.

The U.N. chief said President Hu Jintao and Premier Wen Jiabao told him during his recent visit to Beijing that China will play "an active and constructive role" in the negotiations to reach agreement on a treaty to replace the 1997 Kyoto Protocol which expires in 2012.

Hu and Wen also agreed on the importance of world leaders "showing the way" to a climate deal, he said.

The secretary-general has invited leaders of the 192 U.N. member states to a Climate Summit at U.N. headquarters in New York on Sept. 22. Ban said he expects more than 100 heads of state and government to attend what he predicted will be "the largest gathering of leaders on climate change ever."

Since he took over the helm of the United Nations 2 1/2 years ago, Ban has made climate change his top priority.

He told reporters that his "utmost priority" now is making the Copenhagen meeting a success and announced that he will follow up his recent visits to China and Mongolia focusing on the impact of climate change with a trip to the Arctic polar rim in late August for a firsthand look at the melting sea ice. To keep up the momentum, he will then attend the World Climate Conference in Geneva organized by the World Meteorological Organization.

A new global warming treaty would build on the Kyoto treaty's mixed success in requiring that 37 industrialized nations reduce greenhouse gas emissions an average of 5 percent below 1990 levels by 2012. The United States has said it is committed to reaching a deal to reduce greenhouse gases in Copenhagen as long as other major polluters such as China and India do their part as well.

But at U.S.-China talks in Washington this week, China did not signal any change in its refusal to agree to a specific cap on greenhouse emissions. The two sides did sign a document that U.S. Secretary of State Hillary Clinton said would create a platform for future cooperation on climate change heading into the Copenhagen negotiations.

China's chief climate change official, Xie Zhenhua, told reporters earlier that rich countries should take the lead in reducing emissions and should help poorer countries by providing money and technology to deal with the problem. India told Clinton earlier this month it won't accept any limits on its emissions.

Ban said he wants "a fair, effective and scientifically ambitious deal in Copenhagen that can benefit all nations."

"We have the capacity, we have the technology, we have the financing, but simply because of a lack of political will — where leaders are not simply able to look beyond their borders — that's why we have not been able to agree on climate change," he said.