Russian President Vladimir Putin said on Tuesday that Moscow would mull striking the ships of countries backing Ukraine if attacks on Russia’s tanker fleet continue.

“What the Ukrainian armed forces are doing now is piracy,” Putin told reporters in response to a query about attacks on vessels in the Black Sea.

His remarks followed a string of hits on tankers tied to Russia’s so-called shadow fleet which have been linked to Ukraine, though Kyiv has firmly denied responsibility for one of the incidents and refused to issue official comment on the others.

Putin said that Russia would first “expand the range of strikes” on Ukrainian ports and visiting vessels.

He then raised the stakes, adding: “Secondly, if this continues, we will consider the possibility – I’m not saying we will do this, but we will consider the possibility – of retaliatory measures against the vessels of those countries that assist Ukraine.”

“The most radical option is to cut Ukraine off from the sea, then piracy will be impossible in principle,” he added.

Putin finished: “I hope that the Ukrainian military leadership, the political leadership, and those behind them will consider whether it’s worth continuing this practise.”

On Friday, there were almost simultaneous attacks on two sanctioned tankers, Kairos and Virat, off the Black Sea coast of Turkey while they were en route to the Russian port of Novorossiysk.

A source from the Security Service of Ukraine (SBU) claimed responsibility for those attacks, saying: “Modernized Sea Baby naval drones successfully targeted the vessels.”

The source added that the tankers could have been carrying nearly $70 million worth of oil and were allowing the Kremlin to dodge international sanctions.

Kremlin spokesman Dmitry Peskov condemned the incident, calling it “outrageous” and “an encroachment on Turkey’s sovereignty,” while Turkey described the attacks as a “serious threat” to shipping and environmental security.

On Monday, an oil tanker carrying diesel suffered four external explosions near Dakar, Senegal, its manager said, adding that it was working on investigations into what caused the incident.

On Tuesday, a Russian-flagged tanker loaded with sunflower oil was attacked by a drone off the Turkish coast, Turkey’s maritime authority said.

Ukraine firmly denied that it was involved in the incident, with Heorhii Tykhyi, the Foreign Ministry spokesman, writing on social media: “Ukraine has nothing to do with this incident, and we officially refute any allegations of such kind made by Russian propaganda.”

He suggested it may have been a false flag operation by Russia: “Furthermore, the alleged route from Russia to Georgia across Türkiye’s EEZ makes no sense—and suggests that Russia may have staged the whole thing.”

Ukraine has also implemented missile and drone attacks on the Novorossiysk port that have disrupted Russia’s oil shipments in a bid to sap its war chest.

At least one ship manager said that they would cease sending vessels to Russia amid fears over an attack on their freighter, according to Bloomberg.

The tanker attacks have spurred a mixed response, with Estonian Foreign Minister Margus Tsahkna saying on Monday saying that it would be unwise for Ukraine to attack Russian ships in the Baltic Sea as it could lead to a major environmental disaster.

“About 60-plus percent of Russia’s gas and oil exports pass through the Gulf of Finland, and that is an enormous volume, especially in a corridor only about six nautical miles wide. We have not said ‘don’t come here,’ but it would be wise not to, because it really could escalate the situation in the Baltic Sea,” the minister said.

“But let’s be honest: Ukraine has the right to destroy military and strategic targets even on Russian territory. International waters are a bit of a different matter.”

Meanwhile, NATO Secretary General Mark Rutte, the NATO Secretary General, said on Tuesday that he noted the concern expressed by Turkey about security in the Black Sea, but that the incidents were “further evidence of the risks to security” posed by Russia’s decision to invade Ukraine.