Russia's President Vladimir Putin said Russia will have to reduce gas supplies to Europe if Ukraine steals gas. Pipelines that supply Europe crosses Ukraine en route.
In June, Moscow to Ukraine due to mounting debts and pricing disagreements.
Disturbance of Russian gas supplies to Europe has happened two times in the past ten years, in 2006 and 2009. A third of Europe's gas comes from Russia.
between Ukraine and Russia, Ukraine may face energy shortages this winter—further increasing risks to Europe's gas supply.
—Reuters contributed to this report.