Russia detained a Greek-owned oil tanker on Sunday after it left an Estonian Baltic Sea port, the Estonian Foreign Ministry said, adding it had alerted NATO allies to the incident.

On May 13, a mysterious ship named Jaguar sailed through waters near Estonia in the Baltic Sea. This ship, once registered under Gabon’s flag but now sailing without any national flag, was believed to be part of a “shadow fleet.

Russia detained the Liberian-flagged oil tanker Green Admire, which left the port of Sillamae and was sailing through Russian territorial waters, Estonian Public Broadcasting said Sunday, citing the Estonian Department of Transport.