Berlusconi had been scheduled to make the opening speech at a two-day global conference of environment ministers, where he had been expected, as the EU's current president, to hammer home European support for Kyoto.

But in a message, Berlusconi said he was unable to attend because of preparations for a key EU summit in Brussels on Friday and Saturday.

"Unfortunately, the intensive consultations on the European constitution require my personal attention and prevent me from coming today," Berlusconi said.

He hoped the conference would yield results that would "reinforce the credibility of the Kyoto Protocol" and "encourage" its ratification by three major holdouts -- Australia, Russia and the United States.

Green activists described Berlusconi's no-show as a grievous blow in the campaign to save the climate deal from oblivion.

"It's a very, very bad signal," a spokeswoman for WWF Italy said.

"We were hoping for a strong message to Russia. Berlusconi should have lived up to the promise he made" that he would lobby Russian President Vladimir Putin on Kyoto's ratification.

The two-day mustering of signatories to the UN Framework Convention on Climate Change (UNFCCC) is the first since Russia started sending out conflicting signals on whether it would ratify Kyoto, the only global deal to cut greenhouse gases blamed for changing Earth's climate.

UN Secretary General Kofi Annan, in an address read to the meeting, warned that some of the impacts of climate change may already have started to kick in.

"The heightened frequency and intensity of extreme weather events and associated natural disasters that we have seen in recent years -- such as the serious droughts this summer in India and Europe, and the storms that devastated parts of North America -- is consistent with this conclusion," said Annan.

"There is growing concern that this trend is likely to continue."

A total of 188 countries and other entities were being represented at the meeting, about 90 of them at ministerial level.

Diplomats said divisions over Kyoto were so profound that the meeting had been framed to skirt any controversy or decision-making and would instead use "round tables" to air specific problems of climate change.

The Kyoto Protocol is the most ambitious environmental agreement ever attempted, but its future has been darkened by the United States' walkout in 2001 and by Russia's ambiguity.

Sources say Russia's on-again, off-again noises on ratification are linked to demands for concessions from Europe on admission to the World Trade Organisation (WTO).

The pact requires industrialised signatories to cut emissions of six carbon gases by a timetable of 2008-2012 as compared to their 1990 levels.

The European Union championed the Protocol and made concessions to other reluctant countries to get a deal in 2001 that completed all the major points in its highly complex rulebook.

But it was obliged to make further concessions on Tuesday, agreeing to let genetically-modified trees be included in so-called "carbon sinks" -- forests that are planted to soak up CO2 and thus can be offset against emissions targets.

GM plants are being fought by Europe's powerful green lobby as being a potential threat to health and the environment, and surveys show gene technology is widely mistrusted by the European public.

EU Environment Commissioner Margot Wallstrom put a brave face on this, saying that the deal gave "full information, full transparency in order to make an informed choice."

"Countries can say no if they don't like that, that's the thing," she told AFP on Wednesday.

The US delegation, according to diplomats, bluntly gave notice on Tuesday that the United States would fight any unfounded attempt to block GM trees, warning that commercial law "supersedes" environmental law.

SPACE.WIRE