About 50 African countries forced the cancellation of several technical meetings, saying they were only ready to discuss the pledges submitted by the wealthy countries.

Talks were under way to try to resume the closed-door meetings Tuesday, the second day of a five-day meeting to prepare a draft treaty to be adopted at a major U.N. conference next month in Copenhagen.

Delegates said unless the African boycott was settled, it could set back the timetable for concluding a Copenhagen agreement.

The African countries say they are the most vulnerable to climate change yet the least responsible for the accumulation of carbon in the atmosphere that is causing global warming. A landmark 2007 UN report based on the work of about 2,000 scientists predicted Africa will suffer the most from drought and damage to agriculture, as well as from rising sea levels threatening coastal areas and the spread of tropical pests and diseases.

Scientists say industrial countries should reduce emissions by 25 to 40 percent from 1990 levels by 2020, but the targets announced so far by those countries amount to far less than the minimum.

The Copenhagen deal would succeed the 1997 Kyoto Protocol, which called on 37 industrial countries to reduce emissions of heat-raising gases by an average 5 percent below 1990 levels by 2012. It made no demands on major developing countries like India and China. The United States was the only major greenhouse gas emitter to reject the Kyoto accord.

The African boycott suspended talks on technical issues related to emissions reductions. Those included identifying new gases to be regulated in addition to the six greenhouse gases named in the Kyoto pact, discussing how to account for carbon emissions from forests and coming up with rules for rich countries to offset their emissions by investing in green technologies in developing countries.

The US, which says it wants to be part of the Copenhagen deal, has been criticized for delaying any announcement at this week's climate talks of its emissions target. The US delegation says it is waiting for Congress to finish work on climate and energy legislation. Those bills suggest the US would cut emissions only about 4 percent below 1990 levels over the next decade.

On Monday, the US came under renewed pressure to declare its intentions at the UN talks before the decisive Copenhagen meeting from Dec. 7-18.

Danish Environment Minister Connie Hedegaard, who will chair the Copenhagen meeting, noted that President Barack Obama will be in nearby Norway accepting the Nobel Peace Prize while the Copenhagen conference is under way.

She said it was ``hard to imagine'' that Obama, who was cited by the Nobel committee for his climate-friendly policies, would send his delegation to Copenhagen empty-handed.

In London, UN Secretary-General Ban Ki-moon admitted Tuesday that the climate change treaty may not be resolved this year.

Following talks with British Prime Minister Gordon Brown, Ban said nations may be unable to commit to firm emission limits at Copenhagen.

"I'm reasonably optimistic that Copenhagen will be a very important milestone. At the same time, realistically speaking, we may not be able to agree all the words," Ban said.