Estonia said on Thursday that Moscow had briefly sent a military jet into NATO airspace over the Baltic Sea during an attempt to stop a Russian-bound oil tanker thought to be part of a "shadow fleet" defying Western sanctions on Moscow.

Axar.az reports, citing Reuters, Russia, which regards sanctions as a malign attempt to crush its economy, says all its ships have free passage in the Baltic and any attempt to stop them is dangerous.

Estonia's navy said the unflagged Jaguar ship, which went on a UK sanctions list last week, refused to cooperate when asked to stop and was then escorted to Russian waters.

"The Russian Federation sent a fighter jet to check the situation, and this fighter jet violated NATO territory for close to one minute," Estonian Foreign Minister Margus Tsahkna told reporters in Turkiye ahead of a meeting of foreign ministers from the transatlantic military alliance.

"(The) Russian Federation is ready to protect the 'shadow fleet'... The situation is really serious," Tsahkna added.

Estonia said NATO military jets had also taken off to inspect the Gabon-listed Jaguar.