CANCUN, Mexico - A bloc of Latin American countries issued a stern warning to rich nations Friday that unless they commit to new emissions cuts, the UN climate talks in Cancun will fail.

Negotiators from Venezuela, Bolivia, Nicaragua and Ecuador — all members of the leftist ALBA alliance — said they would not accept the refusal by some developed countries to extend their binding emissions targets under the Kyoto Protocol, the climate pact that expires in 2012.

Venezuela and Bolivia were among a handful of countries that blocked a nonbinding climate accord with voluntary emissions pledges from being adopted at last year's U.N. climate conference in Copenhagen. The rules of the talks require consensus.

Without naming them, Venezuelan negotiator Claudia Salerno said "a handful" of developed countries had ruled out a second commitment period under Kyoto. She called their stance "unacceptable" and said it could hold back progress on other issues being discussed in Cancun.

"If there is no second period of Kyoto, it is very difficult that there can be any balanced package" of decisions in Cancun, Salerno said.

The fate of the Kyoto Protocol, or the shape of any agreement that succeeds it, is one of the most divisive issues in the negotiations.

Earlier this week Japan said it was not interested in negotiating an extension of the Kyoto targets, arguing it was pointless unless the world's largest polluters — China is No. 1, and the U.S. No. 2 — also accepted binding targets. U.N. climate chief Christiana Figueres said Russia and Canada also oppose extending their Kyoto targets.

For 13 years, since it was negotiated, the United States has rejected the Kyoto accord, partly because it made no demands on rapidly developing countries like China and India.

Venezuela and Bolivia and other members of the ALBA bloc argue that climate change is the result of a capitalist system and demand steep emissions cuts from industrialized countries deemed to have a historical responsibility for the release of carbon dioxide and other heat-trapping gases into the atmosphere.

Figueres said she wasn't expecting the positions of the ALBA nations and the developed countries to "dramatically change" in Cancun.

"What needs to happen here is countries need to find a compromise," she said.

She and other U.N. officials hope for agreements on secondary issues at Cancun, and expect this central dispute to extend into next year's negotiations.

Delegates at the 193-nation conference are also discussing setting up a "green fund" to disburse aid to poorer countries to reduce their emissions and adapt to climate change; to make it cheaper for developing nations to obtain climate-friendly proprietary technology; and to finalize more elements of a complex plan to pay developing countries for protecting their tropical forests.

European and U.S. negotiators said the discord over extending Kyoto targets could hinder progress on those issues.

"It may be that the problems with Kyoto could completely tie this conference up, but I am very hopeful that that doesn't happen, because I think it would be a huge mistake," U.S. climate envoy Todd Stern said.

EU negotiator Arthur Rung-Metzger urged the ALBA nations to compromise.

"If countries park on extreme positions, it's just not possible to come to a consensus, that is certainly something that is still hanging like a Sword of Damocles over this conference," he said.

As the climate talks drag on, the Earth continues to warm. On Thursday the World Meteorological Organization reported that 2010 is on track to become one of the three hottest years and 2001-2010 the warmest 10-year period on record.

Scientists say a gradually warming earth is expected to bring on droughts and floods with increasing frequency, and a report issued at the conference Friday said about 350,000 lives are at risk annually worldwide from such natural disasters.

Prepared by a group of vulnerable nations headed by the island state of the Maldives and DARA, a Madrid-based humanitarian research group, the Climate Vulnerability Monitor 2010 said the effects of climate change could contribute to the deaths of 5 million people by 2020 and cause as many as 1 million deaths per year by 2030 if global warming isn't slowed.