The latest scientific and economic understanding of global climate change would underpin the new targets, representatives of 160 countries decided at a conference in Bonn.

The talks will likely last at least two years, delegates said.

"This (agreement) makes clear ... that the outcome of this process will be a new set of quantitative caps," Michael Zammit Cutajar, head of the UN group driving the process, told Reuters immediately after the conference approval.

"This is a new phase in the life of the Protocol."

Kyoto obliges 35 rich nations to cut emissions by at least 5.2 percent below 1990 levels by 2008-12.

The Ad Hoc Working Group was set up to chart post-2012 talks at a previous Kyoto meeting held at the end of last year.

The world's biggest polluter, the United States, pulled out of the Kyoto Protocol in 2001 and was not involved in Friday's agreement.