President Vladimir Putin said Russia would seize ships belonging to European countries if they tried to sell cargo confiscated from Russia-linked vessels suspected of belonging to Moscow's so-called shadow fleet.

"This is nothing less than piracy and robbery," Putin said during drills by Russia's Pacific Fleet on August 12, referring to Europe's plans to tighten measures against vessels suspected of helping Moscow evade Western sanctions.

"If this begins to be put into practice, we shall be forced to respond in kind," he added, saying that Moscow would not limit its response to the waters where Russian ships were being detained. He did not provide other details.

Western governments have stepped up efforts to target the shadow fleet -- a network of opaquely owned or insured vessels that Russia has used to keep its oil exports flowing despite sanctions imposed over its invasion of Ukraine.

Putin's statement came after the European Union last month passed a new sanctions package against Russia, including measures allowing member states to sell oil or other cargo seized from sanctioned or detained vessels.

According to European media reports, Swedish court documents showed that Stockholm was planning to transfer to Kyiv a seized Russian ship suspected of transporting grain from Russian-occupied parts of Ukraine.

Days before Putin's threats, the US Senate also approved a sweeping Russia and Iran sanctions package that would give President Donald Trump additional leverage to push Moscow toward negotiations with Ukraine by squeezing its war economy.

Since the beginning of Russia's full-scale invasion of Ukraine in February 2022, energy revenues have remained a crucial source of income for the Russian state and its war effort. Kyiv has sought to curb Russia's ability to finance the war by calling for strict sanctions against its energy sector.

Among other things, the bill -- which has yet to be approved by the US House of Representatives -- targets Russia's shadow fleet, including vessels, owners, operators, insurers, ports, and other intermediaries involved in transporting Russian oil and sanctioned goods.

In recent months, the Ukrainian military has also intensified its long-range attacks on Russia's shadow-fleet vessels and energy infrastructure, a campaign Ukrainian President Volodymyr Zelenskyy has described as Kyiv's "long-range sanctions" against Moscow.

With reporting by AFP and Reuters