The slow pace of progress in United Nations-led climate talks is the fault of leaders distracted by domestic political crises, the United Nations' secretary-general said Tuesday, as he urged them to continue work toward a binding climate deal.

"We should not forsake our common vision to have a legally binding treaty where all the countries big or small can work together to address this issue," UN secretary-general Ban Ki-moon said as talks continued in this port city.

Delegates won't complete that kind of binding deal in
Durban , and even reaching such a deal in the distant future isn't guaranteed. The U.S. has said it could support such an agreement, but might prefer other options such as strong individual commitments to cut emissions.

China caused a stir earlier this week by suggesting it could accept a binding deal after 2020--under very stringent conditions.

Ban also urged signatories of the Kyoto Protocol, a 1997 agreement of developed-world economies to cut emissions, to extend those pledges beyond their expiration date next year.

"We must not leave [a] vacuum between [the] first and second commitment," Ban said. "We must find a way forward for a Kyoto Protocol future."

Canada , Japan and Russia have already said they won't extend their commitment to the protocol. But UN organizers have said the agreement could be kept alive if remaining developed nations continue to cut emissions.

The U.S. has never ratified the Kyoto Protocol.