Russia sent a submarine to escort an empty oil tanker the US military has been pursuing and attempting to seize for weeks, according to US media reports.

The United States has been chasing the oil tanker, formerly known as the Bella 1, since it evaded a partial US blockade around Venezuela and thwarted an attempt by the US Coast Guard to board it late last month.

US officials said the tanker is part of a shadow fleet carrying oil for countries such as Venezuela, Russia and Iran in violation of US sanctions. Tracking data from MarineTraffic showed the tanker nearing Iceland's exclusive economic zone on Wednesday.

Russia sent "a submarine and other naval assets" to escort the tanker, the Wall Street Journal reported Tuesday, citing unnamed US officials.

CBS News said two US officials confirmed "that Russia had sent a submarine and other Russian naval vessels" as escorts.

Russia's foreign ministry earlier Tuesday said it was "following with concern" the US pursuit of the tanker. The ministry told state-run media prior to reports of the escort that the vessel was sailing under the Russian flag and was far from the US coast.

"For reasons unclear to us, the Russian vessel is receiving heightened attention from the US and NATO militaries -- attention that is clearly disproportionate to its peaceful status," the ministry said.

Since being pursued by the US Coast Guard, the vessel has switched its registration to Russia, changed its name to the Marinera and the tanker's crew reportedly painted a Russian flag on the tanker last month.

The developments are the latest in US President Donald Trump's crackdown on sanctioned oil tankers going to and from Venezuela.

The oil tanker now guarded by Russia had been en route to Venezuela but was not carrying cargo before it evaded the US blockade.

It has been under US sanctions since 2024 over alleged ties to Iran and Hezbollah.