Moscow, Russia - Russia said Tuesday the US has not released two Russian crew members of a tanker seized in the North Atlantic despite promising to do so.

The US took over the Russian-flagged Marinera earlier this month, alleging it was part of a shadow fleet of tankers carrying oil to countries such as Venezuela, Russia, and Iran in violation of unilateral sanctions.

"We were assured that a decision has been made at the highest level to secure their release," Russian Foreign Minister Sergei Lavrov told a news conference.

"Unfortunately, the following days showed that this decision is not being implemented. We expect our American colleagues to fulfill their promises that were made to us," he added.

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President Donald Trump's administrations has said publicly that the Marinera's crew could be prosecuted – which Russia said would be "categorically unacceptable."

US forces seized the tanker, which was being escorted by the Russian navy, after chasing it from near the Venezuelan coast.

It was re-flagged and re-named to bring it under Russian jurisdiction in a bid to discourage the US from trying to take it as part of its campaign against Venezuela, which escalated with a violent coup and a partial blockade declared as illegal by a panel of UN experts.