In October 2023, another Chinese ship ruptured an undersea gas pipeline between Finland and Estonia.

The Yi Peng 3 and Eagle S are both suspected of being part of a so-called shadow fleet of oil tankers that Russia is using to avoid Western sanctions imposed since the full-scale invasion of Ukraine.

The EU said it was working on measures including sanctions to target “Russia’s shadow fleet, which threatens security and the environment”.

After several weeks at anchor in the Kattegat strait between Sweden and Denmark, the Chinese tanker was eventually boarded by authorities from Sweden, Denmark, Germany and Finland, but then set sail last week.

By contrast, Finnish authorities said they had boarded the Cook Islands-registered Eagle S in the early hours of Thursday and it was escorted towards the Finnish coast off Porkkala, across the Gulf of Finland from Tallinn.

“Our patrol vessel travelled to the area and could determine visually that the vessel’s anchor was missing,” said Markku Hassinen, deputy head of the Finnish Border Guard, told a news conference.

The Estonian prime minister sought to reassure Estonians on Thursday that they would continue to have secure power supplies.

The two main power companies, Elering and Eesti Energia, had various reserve and back-up power plants, he told reporters.

However, he added that it was impossible to protect every square metre of the seabed at all times.