Russia's lower house of parliament has ratified the Kyoto Protocol - the international treaty on climate change.
Putin's backing for Kyoto has been vital
The United Nations treaty, already backed by 126 countries, needed Russia's support before it could come into force.
The State Duma voted 334-73 to approve the treaty, which calls on signatories to cut their greenhouse gas emissions.
Washington said that it had not changed its position on the pact - and did not intend to sign or ratify the protocol.
"We do not believe that the Kyoto Protocol is something
that is realistic for the United States and we have no
intention of signing or ratifying it," State Department spokesman Adam Ereli said.
The protocol still has to pass through the upper parliament and be signed into law by President Vladimir Putin.
Both further stages should be a formality, says the BBC's Sarah Rainsford in Moscow, meaning the Kyoto protocol could get final approval from Russia within the month.
Tipping the balance
Russia's move has been hailed by activists.
"We'll toast the Duma with vodka tonight," Greenpeace
climate policy adviser Steve Sawyer said.
"The entry into force of Kyoto is the biggest step forward
in environmental politics and law we have ever seen,"
said Jennifer Morgan, director of the World Wide Fund for Nature (WWF) conservation group's climate change programme.
European Commission president Romano Prodi said: "We are happy that the Russian Duma has decided to ratify. I would also like to thank President Putin for his personal support for this process."
"We hope that the United States will now re-consider its
position," he added, in quotes carried by the AFP news agency.
The US, world's biggest polluter, pulled out of the treaty in 2001.
Friends of the Earth International called for "international
pressure" to encourage the US and Australia to join.
For Russia, backing the pact is more a political move than an environmentally friendly one, our correspondent says.
The Russian Duma was never expected to resist ratification as it is filled with Vladimir Putin's allies and the powerful president made his support for Kyoto clear last month.
President Putin agreed to fast-track the ratification of Kyoto in May, when the EU promised to support Russia in its bid to join the World Trade Organisation.
However, some officials have argued it could hinder economic growth.
Mr Putin's own economic adviser, Andrei Illarionov, fiercely opposed ratification.
Buying and selling
Although it was adopted nearly seven years ago, the Kyoto Protocol had until now remained a statement of intent, rather than a legally binding document.
To come into force, it needed to be ratified by developed nations that account for at least 55% of global greenhouse emissions.
After the US pulled out, that figure could only be reached with the support of Russia, which accounts for 17% of world emissions.
Scientists say greenhouses gases may have to be cut by up to 60%
Within 90 days of Russia's ratification, Kyoto signatories must start making cuts that will reduce emissions of six key greenhouse gases to an average of 5.2% below 1990 levels by 2012.
Countries which fail to meet the targets will face penalties and the prospect of having to make deeper cuts in future.
BBC science analyst Tracey Logan notes that many experts believe that Kyoto will be largely ineffective as the world's two biggest emitters, the US and China, will not cut their outputs.
Although China did sign the protocol, as a developing country it is not yet required to begin reducing emissions.