The head of the United Nations body overseeing the Copenhagen climate-change talks says the Kyoto protocol must be retained in the final deal.
Negotiations at the conference have stalled over whether the protocol should be expanded or replaced by a wider treaty including the United States and China.
Industrialised nations such as the US are insisting that a successor to Kyoto must be created to deal with the growing emissions from China and India.
But the executive secretary of the UN's framework convention for climate change, Yvo de Boer, says Kyoto must be extended, as it will take many years to develop a replacement.
Tuvalu still pushing its proposal
Tuvalu says it is still pushing for its proposal for a legally binding agreement to be openly debated at the conference.
The proposal calls for stronger emission cuts, global temperature rises to be limited to 1.5 degrees celsius, and carbon dioxide concentrations to be limited to 350 parts per million.
Negotiations stalled on Thursday after more industrialised developing nations opposed Tuvalu's move to have the proposal openly debated.
But Tuvalu's chief negotiator, Ian Fry, says it had to seize the opportunity to push for a legally binding agreement, as the conference had appeared to be settling for producing a framework for future agreement.
Mr Fry says the Copenhagen conference needs to be more ambitious about what it can achieve.