Germany's gas stocks have fallen to a "worrying" level, an economy ministry spokeswoman said Wednesday, as fears over a possible invasion of Ukraine by Russia put further pressure on energy supplies.

"Of course we are monitoring the situation of the storage levels and that is certainly worrying," said the spokeswoman during a regular government press conference.

Stocks were now at 35-36 percent, under the "critical level" of 40 percent which the German government deems is necessary to withstand seven straight days of an extreme cold snap.

To overcome a 30-day streak of more moderate cold weather, the storage should be half full.

Stocks never slid below 71 percent in 2020, according to data from the industry group Gas Infrastructure Europe.

With around 40 percent of gas consumed in Europe coming from Russia, Moscow is suspected of taking advantage of the tensions on the world market to reduce supply and drive up prices.

In an interview this week with Die Zeit weekly, EU leader Ursula von der Leyen said that there are "increasingly signs that the Kremlin is using gas deliveries as political leverage."