Several countries in Europe have stopped ships transporting Russian oil in violation of European sanctions.
New sanctions adopted last month allow EU countries to sell oil - a major source of income for Russia - or other cargo seized from the ships.
Russian President Vladimir Putin has called the new sanctions "piracy", writes the AFP news agency.
"We will be forced to respond in kind," he said on Wednesday from a cruiser off Sakhalin Island, where the Russian navy was conducting military exercises.
Moscow will act “wherever we ourselves deem it necessary and appropriate - anywhere,” he added.
Will hand over ship
Sweden plans to hand over a seized Russian ship, the Caffa, which is located in the port of Trelleborg, to Ukraine. The ship is suspected of having transported grain from occupied parts of Ukraine.
It will be handed over to Ukraine. How and when is not something we are saying. That is part of the secrecy surrounding the whole thing, State Prosecutor Håkan Larsson told TT.
The prosecution has asked the police to enforce the decision. For now, it remains in Trelleborg, as far as he knows.
Why is it confidential?
The ship is to be handed over in connection with an ongoing investigation abroad. Ukraine has requested confidentiality.
“The Russians don’t like it”
Prime Minister Ulf Kristersson is not at all surprised by Putin's threat, which he says is reminiscent of previous threats but expressed in different words. Moscow is "incredibly irritated" by the shadow fleet ships that Sweden is stopping.
The Russians don't like that. Then they want to raise the tone to scare the countries that are on Ukraine's side. That's the whole idea behind this. But we won't let ourselves be scared, he says.
When asked whether we need to take Putin's threats seriously, Kristersson says that Russia is a "dangerous" and "neglected" country that does not like those who support Ukraine.
But we have taken that into account.
