Russia has threatened to block Western flights over its airspace if the European Union brings in more sanctions over the Ukraine crisis, in a step that prime minister Dmitry Medvedev warned could force "struggling" airlines out of business.
This comes as European leaders have adopted new sanctions that would come into effect "in the next few days" aimed at Russia's energy sector. EU Council President Herman van Rompuy said leaders were "ready to review" the measures depending on how the ceasefire goes, which was agreed between Russia and Ukraine on Friday.
The measures, he said, were aimed at "promoting a change of course in Russia's actions destabilising eastern Ukraine".
However, Medvedev told the Russian business newspaper Vedomosti that: "If there are sanctions related to the energy sector, or further restrictions on Russia's financial sector, we will have to respond asymmetrically.
The Russian premier suggested that the need to "bypass our airspace ... could drive many struggling airlines into bankruptcy". "This is not the way to go," he stressed. "We hope our partners realise this at some point."
Western airlines would undeniably suffer if Russia shuts down its airspace as they would have to spend much more on fuel in order to take longer routes avoiding the country. At the same time the move would hurt Russia as it would lose out on royalty revenues from international airlines flying through its airspace.
This comes as a think-tank has suggested Europe could cut its dependence on gas from Russia with a major push on energy efficiency.
If the European Union made improving energy efficiency the centrepiece of its strategy on energy, it could cut its reliance on gas by a third by 2030, equivalent to the proportion of the EU's gas demand met by imports from Russia.
A move to significantly boost energy efficiency in appliances, buildings and industry across Europe would also slash the EU's fuel bill by 500 billion euros (£400 billion) up to 2030, a report from think-tank IPPR said.
IPPR research fellow Joss Garman said: "The crisis in Ukraine has reignited the debate in Europe over whether the package of energy policies that the continent's leaders are aiming to agree in October should include a binding 2030 target on energy efficiency.
"This is because the countries that are most dependent on Russian gas are also the least fuel-efficient, and improvements in energy efficiency could vastly reduce the scale of our dependency on Russia."
He urged: "European leaders should adopt a new, binding EU-wide target for energy efficiency of 35% by 2030.
"This level of ambition would enable Europe to cut gas imports by a third, equivalent to the proportion of the EU's gas demand that is currently met by Russia. Britain should overcome its aversion to an energy efficiency target as part of its broader response to Russian aggression."
A spokesman for the Department of Energy and Climate Change said: "We are committed to energy efficiency and support ambitious EU energy efficiency measures to promote economic growth, reduce costs for households and businesses, improve energy security and support action to decarbonise cost-effectively.
"We are concerned that an EU energy efficiency target for 2030 would not allow member states the flexibility to choose the most cost-effective pathway to reducing greenhouse gas emissions and increase the costs of delivering the overall 2030 package."