The treaty, which has been opposed by the United States, needs Moscow's approval to come into force.

"The Russian government is meticulously examining this question and is studying all of the difficult problems associated with it," Putin said on Monday.

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

The Kyoto protocol, signed in 1997, provides for a worldwide reduction in the emission of greenhouse gases, especially carbon dioxide, held responsible for global warming.

US refusal

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

With the United States refusing to ratify the treaty, Russia's signature is needed to pass the threshold.

Putin said "restrictions should not be enacted that would impede economic growth and social development".

His words dealt a blow to Kyoto supporters, who had been hoping to convince Russia to ratify the accord during this week's conference.

"I'd hoped for a more precise signal on when Russia would be ready to ratify the Kyoto Protocol because our process on climate change is really waiting for that," said Joke Waller-Hunter, executive secretary of the UN Framework Convention on Climate Change (UNFCC).

Backroom negotiations

"We still do hope that Russia will ratify the Kyoto protocol as soon as possible," European Commission spokesman Reijo Kempinnen said in Brussels.

Observers said Putin's comments reflected backroom negotiations that Russia was conducting on the pact.

George Bush refused to ratify the
Kyoto protocol of 2001

"There is political haggling going on," ecologist Alexei Yablokov told Moscow Echo radio.

"Russia wants to extract the maximum political advantage from the signing of the protocol."

In the past few days, Russian and foreign experts said Moscow would base its decision on economic and political criteria, rather than purely ecological considerations.

Pollution quotas

An official in the presidential administration said last week Russia would ratify Kyoto only if it received firm guarantees on investment and on the sale of emission rights.

European officials have already ruled out such a prospect as unrealistic.

The Kyoto treaty requires industrialized countries to stick to pollution quotas - the amount of pollution it can discharge into the atmosphere - based on a 1990 benchmark.

It also contains a mechanism by which nations can trade their quotas.

Contradictory statements

Because much of Russia's industry has gone offline since 1990, the treaty favours Russia - by 2010 its CO2 emissions will be between 11 and 25% below the benchmark 1990 levels.

In other words, Moscow would have pollution quotas for sale once the treaty enters into force.

In September 2002 Putin hinted strongly at a Johannesburg summit that Russia would eventually ratify the pact.

But since then, Russian officials have issued a series of contradictory statements.