Climate negotiators from more than 100 countries are struggling to reach a broad agreement on a new global treaty to further cut carbon emissions.

Top United Nations climate official Yvo de Boer played down talk of a stalemate as a week-long U.N.-sponsored conference in Vienna moved into its final hours.

But environmental groups accused five countries - Canada, Japan, New Zealand, Switzerland and Russia - of blocking agreement on a target of reducing emissions by up to 40 percent (compared to 1990 levels) by 2020.

The conference is the forerunner to a global meeting of environmental ministers in Indonesia late this year. There, the ministers are expected to launch two years of talks aimed at replacing the Kyoto protocol, which binds 35 nations to cut carbon emissions by five percent by 2012.

The United States has rejected the 1997 Kyoto document, arguing that it favors such developing countries as China and India. However, President Bush has voiced willingness to join a new, long-term global treaty.