Russian President Vladimir Putin has said his country remains undecided on whether or not to sign the Kyoto agreement on curbing greenhouse gas emissions.
Much of Russia's industry has been lost since communism collapsed
Opening a major international conference on climate change in Moscow, he said the government was still studying the protocol.
Russia's approval is vital for the 1997 pact to acquire the force of international law, after the United States pulled out two years ago.
Mr Putin had been urged to use the conference to confirm Russia's ratification and his comments have drawn protests from the United Nations, European Union and environmentalists.
To come into effect, the protocol requires the ratification of countries
representing at least 55% of the global total of carbon
With the US refusing to take part, all the other major industrial powers must ratify the agreement for the quota to be reached.
Despite an apparent assurance a year ago that it would do so, Russia has so far failed to ratify.
The environmentalist group Greenpeace warned that "[Mr Putin's] stalling could now derail the entire process".
UN Secretary General Kofi Annan urged Russia to immediately approve the agreement.
"I join people throughout the world in eagerly awaiting ratification by the Russian Federation, which will bring the protocol into force and further galvanise global action," he said, in a message to the conference.
The EU, which plans to limit emissions from its own industries from 2005, also reiterated its call for Russia to sign up.
Mr Putin was ambiguous about his views on Kyoto.
"[Critics of the pact] often say, half-jokingly and half-seriously, that Russia is a northern country and if temperatures get warmer by two or three degrees Celsius it's not that bad - we could spend less on warm coats and agricultural experts say that grain harvests would increase further," he told the conference.
"That may be so, but... we must also think what consequences we will face in certain regions where there will be droughts and where there will be floods," he added.
BBC environment correspondent Tim Hirsch says international observers are puzzled as to why Russia has such a problem with Kyoto since, on the face of it, the country has secured an extraordinarily good deal from the agreement.
Its target for the period 2008-12 is to keep emissions of carbon dioxide and other gases linked to climate change at the same level as in 1990, compared with an average cut of just over 5% for the industrialised world as a whole.
Climate change means wetter winters and drier summers for some
But since 1990 coincided with the collapse of traditional state-subsidised industry after the demise of the Soviet Union, emissions are already much lower than they were - not because factories are a lot cleaner, but simply because there are fewer of them.
Under the Kyoto system, this leaves Russia with "spare" pollution allowances which it can sell to other countries to help them fulfil their own targets.
This provides Russia with an opportunity to attract considerable foreign investment to renew its ageing energy system.
Many countries will still struggle to achieve the cuts to which they are pledged, so there is likely to be international demand for Russia's allowances.
Our correspondent says Russia's motives could be brinkmanship - waiting for the best possible financial deal; a response to quiet pressure from the Americans keen to see Kyoto collapse; or the result of in-fighting between various parts of the complex government machine.