Western sanctions imposed on Russia for invading Ukraine and aimed at cutting its oil revenues have led to the rise of a vast "shadow fleet" of tankers helping Moscow keep its crude exports flowing.

Estonia warned on Thursday that Russia appears willing to defend with military force its shadow fleet of aging tankers dodging international sanctions to keep oil revenue and equipment flowing, even through the territorial waters of European countries.

Russia deployed a fighter jet in NATO airspace this week after Estonia tried to inspect a so-called shadow fleet tanker passing the EU-member’s economic area, Estonia’s Foreign Minister Margus Tsahkna said.