Japan, Canada and Australia are undermining talks on a treaty limiting emissions of ``greenhouse gases'' with new demands, environmental activists charged Wednesday.

After the United States disappointed delegations by renouncing the 1997 pact without offering an alternative, efforts to curb emissions that are believed to be heating up the atmosphere are running into further problems.

With the United States standing aside, Japan's role is crucial. The accord can only enter into force if backed by 55 countries, representing 55 percent of the industrialized world's emissions. If Japan pulls out, the second target can't be reached.

Japanese Prime Minister Junichiro Koizumi rattled European leaders last week by suggesting that, after the U.S. pullout, an agreement may not be possible before autumn.