France said on Monday it had detained a Russia-linked oil tanker in the Atlantic over the weekend, with the Kremlin comparing the latest seizure aimed at tackling Moscow's sanctions-busting shadow fleet to "piracy".Since September, France has boarded three other ships believed to belong to the shadow fleet, used by Russia to circumvent Western sanctions on its fossil fuel exports imposed over the Kremlin's 2022 invasion of Ukraine. The Tagor was detained on Sunday morning in international waters with the help of Britain and other partners, after its Russian captain repeatedly refused to comply with orders, prosecutors said. "We consider these acts illegal. They border on international piracy," Kremlin spokesman Dmitry Peskov said. "Russia is taking measures to ensure the safety of its cargo". Suspected of carrying Russian or Iranian oil despite international sanctions, the Tagor is linked to petroleum shipping magnate Mohammad Hossein Shamkhani, according to open-source database Opensanctions.org.According to French authorities, the Tagor was on its way from Murmansk in northwestern Russia when it was boarded.The ship was falsely flying a Cameroonian flag and was heading toward Limbe, a seaside city in the west of the African country, said a spokesperson for France's Atlantic maritime prefecture."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," said French President Emmanuel Macron.He posted a video that authorities said was of the seizure, which showed commandos rappelling from a helicopter onto a ship.The Atlantic maritime prefecture said the interception had taken place more than 400 nautical miles (740 kilometres) west of Brittany."The examination of the documents confirmed doubts about the irregularity of the flag being flown," the prefecture said.The ship, which had 23 crew members, was "being escorted by the French navy to an anchorage point for further checks", the prefecture said.When asked about the tanker's ties to Shamkhani, officials declined to comment.Shamkhani is the son of security official Ali Shamkhani, who was an adviser to the former Iranian supreme leader Ali Khamenei, both of whom were killed on February 28, the first day of the US-Israeli attacks that started the Middle East war.- Boarding 'proved necessary' - The Russian embassy in France said it had requested information from the French authorities about the makeup of the crew."No notifications have been provided by the French side regarding actions taken against this vessel," the embassy said on its Telegram channel. The tanker has flown the flags of Madagascar, the Marshall Islands and Panama.