A senior adviser to President Vladimir Putin said Tuesday that Russia cannot ratify the Kyoto Protocol limiting greenhouse gas emissions, dealing a mortal blow to the pact that required Russia's ratification to take effect.

"In its current form, the Kyoto Protocol (search) places significant limitations on the economic growth of Russia," Putin's economic adviser, Andrei Illarionov, told reporters in the Kremlin. "Of course, in this current form this protocol can't be ratified."

Putin had previously cast doubts on Moscow's willingness to ratify the protocol, but hadn't ruled out ratification completely.

The 1997 Kyoto Protocol calls for countries to reduce their level of greenhouse-gas emissions, which are seen as a key factor behind global warming.

To come into force, the pact must be ratified by no fewer than 55 countries, accounting for at least 55 percent of global emissions (search) in 1990. Under the treaty's complex rules, the minimum can now only be reached only with Russia's ratification because the United States and several other nations have rejected the treaty.

Russia's reluctance to ratify the pact despite its earlier pledge to do so has vexed Kyoto's European and U.N. backers, who warned Moscow that it would lose politically and economically if it fails to ratify Kyoto.

But Illarionov, who made his comments on the sidelines of Putin's meeting with European business executives in the Kremlin, said firmly that the pact was against Russian interests.

"It's impossible to undertake responsibilities that place serious limits on the country's growth," Illarionov said. He added that it would be unfair to Russia to curb emissions and stymie its own growth while the United States and other nations which account for the bulk of global emissions refuse to join the pact.

The protocol's proponents see Kyoto as a vital first step in cutting emissions, warning that failure to quickly put it into force would trigger a dangerous, steep rise in greenhouse gas concentrations that would be far more difficult to control in the future.