COPENHAGEN - China's top climate envoy called on President Barack Obama to increase a U.S. offer to cut greenhouse gases, and said it would discuss a 2050 emissions goal only if rich nations offered more cash and carbon cuts.

Xie Zhenhua said developed nations must commit to cuts of at least 40 percent by 2020 from 1990 levels. He said Beijing was aiming for a legally binding treaty from the December 7-18 talks, although hosts Denmark have said that will be impossible.

A successful outcome from the summit largely depends on agreement between the United States and China, which together generate 40 percent of global carbon emissions.

But negotiations have been bogged down for months by rifts between developed and developing nations over who should cut emissions, by how much, and who should pay.

I do hope that President Obama can bring a concrete contribution to Copenhagen, Xie said in a rare interview.

Asked if he meant something more than Obama has proposed so far, a 3 percent cut from 1990 levels by 2020, Xie said: Yes.

The whole world is watching the United States, and as long as they take on a good leadership role, then I think that we can make a large step forward in combating climate change.

The head of China's delegation, who is deputy chairman of the powerful National Development and Reform Commission (NDRC), called for stronger action from rich nations a day after a senior member of his delegation slammed their existing commitments as unambitious and deceptive.

Xie initially told Reuters rich countries should make emissions cuts of 25-40 percent versus 1990 levels by 2020, but clarified later that China was sticking to its past insistence of cuts of at least 40 percent.

2050 GOAL POSSIBLE

Xie ruled out signing up to a long-term emissions cutting goal favored by developed nations unless they took stronger steps to cut their output of greenhouse gases in the shorter-term and provided sufficient, additional and sustainable financial and technology help for poor countries.

We do not deny the importance of a long-term target but I think a mid-term target is more important. We need to solve the immediate problem.

If the demands of developing countries can be satisfied I think we can discuss a (2050) emissions target, he added.

He rejected a current U.N. proposal for fast-track funding of $10 billion a year from 2010-2012 as not enough. China wants developed countries to provide assistance worth 1 to 1.5 percent of their national income.

I think there is a big gap between what has been proposed by the developed world and what is expected by the developing world or by scientific research, he said.

Xie said he preferred a final, legally binding agreement at the meeting in Copenhagen, and it must respect previous United Nations agreements including the Kyoto Protocol and a road map to a deal laid out in Bali two years ago.

Hosts Denmark say time has run out to agree a full text and are pushing instead for a strong political agreement next week, which could then be pinned down in a legal text in 2010.

Many developing nations fear the rich world is trying to undermine the role of the United Nations in the fight against climate change, in a bid to make it easier to whittle down their emissions and financial responsibilities to poor countries.

China Barack obama Climate change