Sweden's prosecution authority is investigating the captain of a stateless vessel in Swedish waters of the Baltic Sea, it said on Friday, after the coastguard boarded and took control of the ship in the second such incident in under a week.
The captain, a Russian citizen, is being investigated on suspicions of the use of false documents, serious crimes and violations of Sweden's maritime act, the prosecution authority said.
"What we are doing now is, among other things, to continue with the search on board, conduct interrogations and investigate suspected false documents," senior prosecutor Adrien Combier-Hogg said in a statement.
So far, no one has been detained in the case, he added. The 228-metre-long (250 yards) tanker Sea Owl I was flying the Comorian flag, and the coastguard on Thursday said it suspected the ship was sailing under a false flag. The ship is also on the sanctions list of several countries, including the EU.
"The threats to maritime safety and the environment are too high," Daniel Stenling, deputy chief of operations at the coastguard, said on Thursday. "Therefore, there is reason to intervene against the vessel."
Sweden's minister for civil defence, Carl-Oskar Bohlin, said in a post on social media that the ship was suspected of belonging to the Russian shadow fleet.
The boarding took place off the coast of the southern Swedish town of Trelleborg.
The Russian embassy in Stockholm did not immediately respond to a request for comment when contacted by Reuters via phone and email. Russia has called seizure of its vessels an act of piracy.
Last Friday, the Swedish coastguard boarded the ship Caffa, which was sailing under a Guinean flag, also near Trelleborg.
(Reporting by Supantha Mukherjee in Stockholm, Louise Rasmussen in Copenhagen; Editing by Chris Reese)
