NATO Secretary-General Jens Stoltenberg expressed concern on January 30 about Europe's gas dependence on Moscow as fears mount of a Russian military escalation in Ukraine.
He said there was consensus among the military alliance's 30 members on the need to diversify energy supplies.
The European Union depends on Russia for around one-third of its natural-gas supplies, and a current shortage amid chilly winter temperatures is already making importers nervous.
"We are concerned about the energy situation in Europe because it demonstrates the vulnerability of being too dependent on one supplier of natural gas, and that's the reason why NATO allies agree that we need to work and focus on diversification of supplies," Stoltenberg said.
Stoltenberg's warning comes with more than 100,000 Russian troops, tanks, and equipment amassed near the border with non-NATO member Ukraine, a post-Soviet transit country for Russian energy supplies to Western Europe that's been locked in a seven-year war against Russia-backed separatists.
Kyiv has consistently railed against Western cooperation to support Moscow's efforts to bypass its traditional gas export routes through Ukrainian territory, knowing its own supplies and billions in transit fees are on the line.
Analysts and a number of NATO governments regard the recently built Nord Stream 2 pipeline as a Russian path to boosting European gas dependence and delivering a costly blow to Kyiv.
Also on January 30, the German regulator said that a locally based subsidiary of Russian gas giant Gazprom still faces hurdles before the controversial Nord Stream 2 pipeline to deliver Russian gas via the Baltic Sea can begin operating.
German Federal Network Agency President Jochen Homann told the FAZ broadsheet that "further steps are missing" before Gazprom's nascent local subsidiary, Gas For Europe, based in Schwerin, can be added to the commercial registry.
Homann predicted in an interview to be published on January 31 that a "conclusion will unlikely be possible in the first half of the year."
An EU gas directive requires the operation of Nord Stream 2 and the distribution of its gas to be managed separately, an obligation that created obstacles in November for Swiss-based Nord Stream 2 AG.