Live updates: follow the latest news on Russia-Ukraine
Authorities in Hamburg impounded Russian billionaire Alisher Usmanov’s superyacht Dilbar after determining it was legally owned by his sister, who is also subject to western sanctions over the war in Ukraine.
The 156-metre vessel, the world’s largest by volume, had been undergoing refitting in the northern German port city.
With a 25-metre swimming pool and two helipads, it is valued at between $600 million and $750m, the US Treasury says.
Germany’s federal crime office the BKA said on Wednesday that despite efforts at “offshore concealment", it had determined that the yacht’s owner was Mr Usmanov’s sister, Gulbakhor Ismailova.
“The luxury yacht Dilbar is therefore subject to sanctions law and was able to be legally impounded in Hamburg,” the BKA tweeted.
The yacht could not be “sold, rented or pledged as collateral", a BKA spokesman told DPA news agency.
The move underscores the wider effects of the penalties levied by Europe and the US on ultra-rich Russians considered to have close ties to President Vladimir Putin.
Superyachts and other luxury possessions of Russia’s elite have drawn especially intense scrutiny since the country’s invasion of Ukraine.
Mr Usmanov owns a major stake in USM, a Russian investment group with holdings in Metalloinvest, one of the world’s largest iron ore producers, and telecommunications company MegaFon.
He is the sixth-richest Russian, with a fortune of $19 billion, the Bloomberg Billionaires Index shows.
The yacht is named after his mother.