The Russian government has approved the Kyoto Protocol on climate change and sent it to parliament to be ratified.
Putin backs Kyoto - but his top economic aide opposes it
Until now, Moscow has wavered over the treaty, which cannot come into force without Russian ratification.
The Kyoto Protocol sets targets for greenhouse gas emissions, which many scientists believe cause global warming.
Moscow's decision was greeted with delight by the European Union and environmental campaigners.
The necessary law on ratification is set to pass through the Russian parliament unhindered and, in theory, the treaty could come into force within three months.
The lower house, the State Duma, is dominated by the pro-Putin United Russia party.
European Union Environment Commissioner Margot Wallstrom told the BBC: "We are very excited today - we have to wait [for] procedures in the Duma, but it looks very good."
And UK Environment Secretary Margaret Beckett praised the Russian move as "a vital step forwards for global efforts to tackle climate change".
Japanese Prime Minister Junichiro Koizumi added his praise, saying the "prevention of global warming is a very important and difficult issue".
Bryony Worthington of environmental campaign group Friends of the Earth expressed delight at the Russian decision, telling the BBC: "It will increase pressure on countries like the US and Australia, who have so far remained outside the only international agreement to curb greenhouse gas emissions."
"It has to be recognised that Kyoto is only the first step and discussions must begin immediately on what happens after Kyoto," she added.
Interfax news agency said that, according to the government decision, ministries linked to the environment had been given three months to work out a series of practical measures arising from Russia's obligations.
Change of heart
Since the US, the world's biggest producer of greenhouse gases, pulled out three years ago, the treaty has been dependent on Russian ratification. Russia accounts for 17% of world emissions.
President Putin ended the confusion over Russia's stance in May, when he spoke of his desire to see the treaty ratified.
But divisions remained among his aides.
His chief economic adviser, Andrei Illarionov, said the treaty would stifle economic growth.
Kremlin economists have questioned how Russia could reduce greenhouse gas emissions when it is enjoying an industrial revival and has set itself the target of doubling GDP within a decade.
This week, top Russian scientists advised against ratification, claiming there was no evidence linking greenhouse gas emissions to climate change.
But the deciding factor appears to be not the economic cost, but the political benefits for Russia, correspondents say.
In particular, there has been talk of stronger European Union support for Russia's bid to join the World Trade Organization, in response to its ratification of the treaty.