Denmark's maritime traffic agency and Sweden's Maritime Authority on Monday reported a "dangerous" gas leak in the Baltic Sea close to the route of the inactive Nord Stream 2 pipeline, which experienced an unexplained drop in pressure.

The leak, southeast of the Danish island of Bornholm, "is dangerous for maritime traffic" and "navigation is prohibited within a five nautical mile radius of the reported position," the agency warned in a notice to ships.

Authorities in Germany, where the undersea pipeline from Russia makes land, said the energy link had experienced a drop in pressure, while its operator suggested that a leak may be the reason.

A spokeswoman for the German Ministry of Economy indicated in a statement that there was "no clarity" over the cause of the pressure change.

The pipeline operator confirmed in a statement that the drop had been registered "overnight" into Monday and reported to national marine authorities.

Nord Stream 2's operator mentioned pressure in the pipeline dropped from 105 to seven bars overnight.

"It is relatively likely that there's a leak" in the underwater pipeline, Nord Stream 2 spokesman Ulrich Lissek told AFP.

He noted that "The pipeline was never in use, just prepared for technical operation, and therefore filled with gas."

Read more: Gazprom: Launch of Nord Stream 2 could resolve EU energy crisis

Berlin suspects a "targeted attack": German newspaper

Following the incident, German newspaper Tagesspiegel claimed Monday that Berlin is convinced that the loss of pressure in the three natural gas pipelines between Russia and Germany was not a coincidence and suspects a "targeted attack".

The German newspaper quoted an informed source as saying that the German government and agencies investigating the incident "can’t imagine a scenario that isn't a targeted attack."

"Everything speaks against a coincidence," the source said.

Tagesspiegel indicated that for a deliberate attack on the bottom of the sea to happen, it has to involve special forces, navy divers, or a submarine, adding that German authorities are reportedly examining two possible explanations for the incident. The first suggests that "Ukraine-affiliated forces" could be behind the attack, while the second suggests that Russia carried out the attack as a "false flag" to blame Ukraine.

The Nord Stream 2 pipeline, which runs parallel to Nord Stream 1 and was intended to double the capacity for undersea gas imports from Russia, was blocked by Berlin in the days before the start of the war in Ukraine.

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. 

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