Freezing weather sweeping across Europe has led to a shortage of vital Russian gas supplies to several countries, officials say.
An EU energy spokeswoman said eight countries had seen a reduction in gas due to increased demand in Russia.
She said the situation was not an emergency but was being monitored.
The cold snap is being blamed for scores of deaths in eastern Europe where temperatures have plunged to below -35C.
Freezing temperatures have spread to Italy and France, and the UK is also on alert for snowfall over the weekend.
"I can confirm that there has been a decrease in gas deliveries in various member states - Poland, Slovakia, Austria, Hungary, Bulgaria, Romania, Greece and Italy," EU spokeswoman Marlene Holzner said.
"It's not a situation of emergency yet," she added.
Correspondents say the sudden drop in Russian gas supplies - which pass through Ukraine - is raising fears of a repeat of a crisis in 2009 when tension between Moscow and Kiev cut supplies to parts of Europe for about two weeks.
Countries including Bulgaria, Serbia and Bosnia are almost completely dependent on supplies via Ukraine.
Gazprom, the Russian gas export monopoly, said on Friday it was supplying as much gas as it could spare.
"We are doing everything possible... all the systems are working in a stable manner," spokesman Sergey Komlev said.
Meanwhile, Ukraine says more than 100 people have died from the freezing weather, most of them homeless.
Authorities have set up nearly 3,000 heating and food shelters across the country and instructed hospitals not to discharge homeless patients.
The Polish interior ministry said that eight people died from the cold on Friday and two others died of carbon monoxide poisoning from charcoal heaters.
In other developments:
- Rome has seen some rare snowfall and Venice's canals have reportedly started to freeze over
- In Bulgaria, parts of the River Danube have frozen over
- More than 20 people have died from the cold in Romania and hundreds of school remain closed
- Officials in Paris say they are trying to cram as many homeless people as possible into shelters as temperatures plummet
Meanwhile, the UK's Met Office has put severe weather warnings in place until Sunday.
It says heavy snow is forecast across much of England and Wales with southern and central areas likely to be the worst hit.