Ukraine has demanded that the U.S. and Germany impose sanctions on Gazprom.
That's after the Russian energy giant implemented a new deal with Hungary that deprives Kyiv of gas supplies.
Under the terms of that agreement, Gazprom will no longer ship gas via a pipeline running through Ukraine.
Instead the gas will go via Serbia and Austria.
That deprives Ukraine of transit fees.
It also means it can no longer import gas from Hungary by reversing the flow.
Signing the deal earlier this week, Hungarian foreign minister Peter Szijjarto said it was all none of Ukraine's business:
"I reject the attempted meddling with Hungary's internal affairs. Providing Hungarians with heating in winter is our job. This cannot be influenced by any other country. What contracts Hungary decides to enter, should not concern any third parties."
Kyiv's ties with Moscow have been in crisis since its annexation of Crimea in 2014.
Now the head of Ukraine's Naftogaz says the new deal constitutes clear use of gas as a weapon.
Yuriy Vitrenko says that requires a response from the U.S. and Germany, who promised to act in such circumstances.
It could be delicate timing for Russia, which wants Berlin to certify the Nord Stream 2 pipeline to Germany that was recently completed.
The project has long been opposed by Washington, precisely because it fears gas supplies could be used as a strategic tool by Moscow.
There was no immediate response to Vitrenko's call from Berlin or Washington.
The Kremlin dismissed it as unfounded.