The US government is auctioning off the $US325 million ($500 million) yacht Amadea, its first sale of a seized Russian luxury ship since the start of Moscow’s invasion of Ukraine.

The auction, which closes on September 10, comes as President Donald Trump seeks to increase pressure on Russian President Vladimir Putin to end the war.

The US has said it’s working with allies to put pressure on Russian oligarchs, some of whom are close to Putin and have had their yachts seized, to try to compel him to stop the war.

The 106-metre-long yacht, seized three years ago and currently docked in the US city of San Diego, was custom-built by the German company Lürssen in 2017. Designed by François Zuretti, the yacht features an interior with extensive marble work, eight state rooms, a beauty salon, a spa, a gym, a helipad, a swimming pool and a lift. It accommodates 16 guests and 36 crew members.

Determining the real ownership of the Amadea has been an issue of contention because of an opaque trail of trusts and shell companies.

The yacht is registered in the Cayman Islands and is owned by Millemarin Investments Ltd., also based in the Cayman Islands.

The US contends that Suleiman Kerimov, an economist and former Russian politician, who was sanctioned by the US in 2018 for alleged money laundering, owns the yacht.

Meanwhile, Eduard Khudainatov, a former chairman and chief executive of the state-controlled Russian oil and gas company Rosneft, who has not been sanctioned, claims to own it.

US prosecutors say Khudainatov is a straw owner of the yacht, intended to conceal the yacht’s true owner, Kerimov. Litigation over the true ownership of the yacht is ongoing.

A representative of Khudainatov said in an emailed statement on Wednesday that the planned sale of the yacht is “improper and premature” since Khudainatov is appealing a forfeiture ruling.

“We doubt it will attract any rational buyer at fair market price, because ownership can, and will, be challenged in courts outside the United States, exposing purchasers to years of costly, uncertain litigation,” said the representative, Adam Ford.

The yacht has been virtually untouched since the US National Maritime Services took custody of it in 2022. To submit a sealed bid on it, bidders must put in a $US11.6 million deposit, to be considered.

Ford said Khudainatov would go after any proceeds from the sale of the yacht, estimated to be worth $US325 million.

“Should the government press ahead simply to staunch the mounting costs it is imposing on the American taxpayer, we will pursue the sale proceeds, and any shortfall from fair market value, once we prevail in court,” Ford said.

An American aid package for Ukraine signed into law last May gave the US the ability to seize Russian state assets in the US and use them for the benefit of Kyiv, which was attacked by Russia in February 2022.