"The Russian government is meticulously examining this question and is studying all of the difficult problems associated with it," Putin said at the opening of the five-day international conference on climate change.

"The decision will be taken at the end of this work and in conformity with Russia's national interests," he said.

Russian ratification of the 1997 treaty is essential for it to come into force.

The Kyoto protocol provides for a worldwide reduction in the emission of greenhouse gases held responsible for global warming, notably carbon dioxide.

To come into force it requires the ratification of countries representing at least 55 percent of the global total of carbon dioxide emissions.

As the United States has refused to ratify the treaty, Russia's signature is essential if signatory countries are to pass the threshold.

At a summit in Johannesburg in September 2002, Putin and Prime Minister Mikhail Kasyanov hinted strongly that Russia would eventually ratify the pact. But since then, Russian officials have issued a series of contradictory statements.

SPACE.WIRE