A target set by the G8 for developed countries to cut greenhouse gas emissions by 80 percent by 2050 is unacceptable for Russia, President Dmitry Medvedev's top economic aide said Wednesday.

"For us the 80 percent figure is unacceptable and likely unattainable," Arkady Dvorkovich told reporters.

"We won't sacrifice economic growth for the sake of emission reduction," he added.

Dvorkovich declined however to unveil Russia's precise targets, saying that releasing them would be premature.

Dvorkovich also said there was no consensus by which year emissions would have to be reduced. "This question is a mystery for everyone," he said.

"The calculations are being done. There are different scenarios," he said, adding they ranged from 20 percent to 60 percent by 2050.

"Discussions on climate are of political nature and are sensitive for everyone," said the aide, within hours of his boss Medvedev apparently signing up to the deal.

"There remains a lot of questions. No one wants to sacrifice their economic growth."

The Russian official was speaking on the margins of a three-day Group of Eight summit in the earthquake-shattered Italian town of L'Aquila.

G8 leaders agreed on the summit's opening day Wednesday to bear the brunt of steep global cuts in greenhouse gas emissions, agreeing to cut overall world emissions by 50 percent by 2050.

At the same time they called on a broader bloc of developed countries to reduce pollution by 80 percent by the same year.

Medvedev's top economic aide also said the target to reduce emissions by 80 percent as compared to 1990 reflected the position of the European Commission but not the G8 as a whole.

Major developed and developing economies face mounting pressure to make ambitious commitments to cut greenhouse gas emissions with the clock ticking ahead of the key Copenhagen climate change meeting to set international targets.

"We still have the time to agree our positions before Copenhagan," Dvorkovich said.