The French Navy boarded and detained a sanctioned oil tanker linked to Russia's so-called "shadow fleet" in international waters over the weekend, French President Emmanuel Macron said Monday.

The Tagor was intercepted Sunday morning in international waters with tactical support from the United Kingdom and other allied partners. France's Maritime Prefecture of the Atlantic said the Tagor originated from Murmansk, Russia, and was seized around 400 nautical miles (740 km) west of the tip of Brittany.

"It is unacceptable for ships to circumvent international sanctions, violate the law of the sea and fund the war that Russia has been waging against Ukraine for more than 4 years," Macron wrote in a post on X.

It marks the fourth time since September that France has boarded vessels believed to belong to Russia's "shadow fleet." The three previously intercepted ships were permitted to resume their voyages after their owners paid fines.

Vessels belonging to the shadow fleet frequently engage in "flag-hopping" — the practice of repeatedly changing the flags they fly — or utilize invalid registrations to evade international tracking.