The operator said it was “relatively likely that there’s a leak” in the underwater pipeline, which runs beneath the Baltic Sea from Russia to Germany.

Authorities had spotted a “large bubble field near Bornholm”, a Danish island in the Baltic, Nord Stream 2 spokesman Ulrich Lissek told AFP.

“The pipeline was never in use, just prepared for technical operation, and therefore filled with gas,” he said.

There was, however, “no clarity” over the cause of the pressure drop in the underwater link, or whether the issue was related to a section of the pipe in “German sovereign waters”, a spokeswoman for the German economy ministry said.

Officials were working to “clarify the situation,” the spokeswoman said, adding that Danish authorities had been alerted to the issue.

The pipeline, which runs parallel to Nord Stream 1 and was intended to roughly double the capacity for undersea gas imports from Russia, was blocked by Berlin in the days before the invasion of Ukraine. Germany, which was highly dependent on imports of fossil fuels from Russia to meet its energy needs, has since come under acute stress as Moscow has dwindled supplies.

Russian energy giant Gazprom progressively reduced the volumes of gas being delivered via the Nord Stream 1 until it shut the pipeline completely at the end of August, blaming Western sanctions for the delay of necessary repairs to the pipeline.

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Germany has rebuffed Gazprom’s technical explanation for the cut, instead accusing Moscow of wielding energy as a weapon amid tensions over the Ukraine war.

Kremlin representatives have previously suggested that the Nord Stream 2 pipeline should be allowed to go into operation.

It was “technically possible” to continue deliveries, Kremlin spokesman Dmitry Peskov said in August.

Former German chancellor Gerhard Schroeder, who signed off on the first Nord Stream pipeline in his final days in office, has also called on Berlin to reconsider its position on the blocked second link.