Denmark is considering ways to curb a so-called shadow fleet of tankers carrying Russian oil through the Balticthe country’s foreign minister said today, in a move that could increase tensions with Moscow.

Russia sends approx a third of its seaborne oil destined for export, or 1.5% of world supply, through the Danish straits which serve as a gateway to the Baltic, so any attempt to cut off supplies could send oil prices soaring and hurt the Russian economy.

After Western countries imposed a price ceiling on Russian oil in an effort to cut off crucial funds for Moscow’s war in Ukraine, Russia relies on a fleet of tankers that are often old and insured outside the West.

Denmark has assembled a group of allied countries to assess measures aimed at this shadow fleet, Lars Loke Rasmussen told Reuters by email.

He did not say what measures were being considered.

“There is broad consensus that the shadow fleet is an international problem and that international solutions are needed,” Loke Rasmussen said.

“It is important that any new measures can be implemented in practice and are legally sound in terms of international law,” he added.

Countries involved in the talks included other Baltic countries and members of the European Union, the minister said.

Denmark is concerned that old oil tankers carrying oil through its straits pose a risk to the environment.

The Russian embassy in Denmark did not immediately respond to a request for comment.

The news was reported by the Danish newspaper Information and the online media outlet Danwatch.