The big challenge facing the ongoing global climate change talks in Durban is that the principles of the Kyoto Protocol should not be abandoned, said Achim Steiner, executive director of the United Nations Environment Programme.

"The Kyoto principles should not be lost, whether you call it a second commitment period, an extension or whatever is agreed, as long as it keeps the Kyoto Protocol alive, it would be good," Steiner said in an interview on Tuesday.

However, difficulties remain as some countries refuse to alter their positions, and that is holding the negotiations back, he said. "This is the challenge of Durban now."

Liu Zhenmin, China's assistant foreign minister, told reporters on Tuesday that Durban's success would be measured by whether there will be a second commitment period of the Kyoto Protocol.

The European Union has showed a willingness to extend its commitments under the treaty, while Japan, Canada and Russia said they would not join a second commitment phase.

"Even though the United States is not willing to join, even though Japan, Russia and Canada are not willing to join, we do see leadership to try to maintain the validity of international action," said Steiner.

"Leadership is the central part, particularly at a moment when processes are not moving very well," he said. In addition, he said the target for emission reduction under the Kyoto Protocol is insufficient and all countries need to contribute.

"Countries like China and Brazil have started to signal that they are willing to consider binding emission cuts in the future, and these are important signals," he said.

On Monday, China's top climate change official Xie Zhenhua, said the nation is open to a legal framework after 2020 on the principles, based on five preconditions including an extension of the Kyoto Protocol and the principles of "common but differentiated responsibilities".

"I think the principle of 'common but differentiated responsibilities' is not a contested issue Having all countries coming to a legally binding agreement does not contradict the principle," said Steiner.

Besides, he said the Durban meeting should deliver on the green climate fund, despite the worsening eurozone debt crisis and bleak global economic outlook.

"The risks are always there, but let us first open the bank account, then we can debate how (we) will fill the bank account," he said.

If the green climate fund and the international climate agreement are sufficient and credible, then countries will invest in them, he said.

He expects progress will be achieved in Durban in areas such as curbing deforestation and accelerating technology transfer to help developing counties combat climate change.

He Jiankun, director of the Institute of Low Carbon Economy at Tsinghua University, expressed hope that nations can reach consensus on the financing issue.

The green climate fund was agreed at last year's Cancun climate change conference to provide assistance to developing countries.

There are still disputes over how to manage the funds, but countries have no disagreements on the green climate fund itself, He said.