Ukraine on Wednesday said Russia had halted gas supplies through a key transit hub in the east of the country, fuelling fears Moscow's invasion could worsen an energy crisis in Europe.

Ukraine pipeline operator GTSOU said in a statement that Russian state energy giant Gazprom had "stopped supplying gas" to the key Sokhranivka transit point.

The claim came as GTSOU announced late Tuesday it was suspending flows through Sokhranivka citing interference by Russia's invading army.

Also on Tuesday, Ukraine state energy company Naftogaz said it told Gazprom it was no longer responsible for transit of gas through territory occupied by Russian forces, volumes it said accounted for one-third of the total transiting Ukraine to Europe.

Kyiv's announcement has fuelled fears that Russia's invasion of its pro-Western neighbour could further push up prices at a time when they are already soaring, with Germany saying it was monitoring the situation "closely".

"Gazprom turned off the tap" to Sokhranivka, GTSOU said on Wednesday.

The company also said Russia had redirected gas intended for transit through Ukraine to the breakaway republics held by pro-Russian separatists in the east.

GTSOU had promised to temporarily reroute all supplies via another crossing point in the north, Sudzha, to "fulfil its transit obligations to European partners in full".

Svitlana Zalishchuk, a top advisor at Ukraine state energy company Naftogaz, told AFP Russia had increased volumes through Sudzha by 15 percent but warned it was "not enough" to compensate for the drop though Sokhranivka.

Berlin closely monitoring

Figures released by GTSOU on Wednesday showed flows through Sokhranivka had dropped to zero.

It said the amount of gas transiting Ukraine via these routes on Wednesday could fall by 18 percent, or 16 million cubic metres, compared to Tuesday.   

Russia's Gazprom denied there was a case for the Ukrainian operator to declare "force majeure" and said it was impossible to reroute all the supplies.

"It's a political game on their side. They will try to show us as irresponsible, but it is exactly the opposite," Zalishchuk told AFP.

Gazprom told TASS news agency that supplies transiting Ukraine on Wednesday were at 72 million cubic metres in total, compared to 95.8 million cubic metres the day before.

In Berlin, a spokeswoman for the German economy ministry confirmed they were "monitoring the situation closely" and said "Germany's energy security currently continues to be guaranteed".

And the Kremlin insisted Russia "has always reliably fulfilled -- and intends to fulfil -- its contractual obligations".

Ukraine is a major supply route for Russian gas to Europe and the two sides have kept flows going even after the Kremlin sent troops into Ukraine on February 24. 

The European Union is scrambling to lessen its reliance on Russian energy supplies, but it has shied away from imposing sanctions on crucial gas flows.