Police have raided the offices of a South Korean company which claims to have found a treasure-laden shipwreck.
Shinil Group said in July that it had found the Russian cruiser Dmitrii Donskoi, which sank in 1905 and was rumoured to hold gold worth billions of dollars.
Speculation has since spread that the alleged find might have been a scam to trick investors.
Shinil chief Choi Yong-seok has been banned from leaving South Korea.
Treasure hunters have searched for the Dmitrii Donskoi for decades, and the announcement of its discovery in July made headlines around the globe.
Shinil released submarine footage showing what it said were parts of the wreck near the island of Ulleungdo, between South Korea and Japan.
The cruiser was scuttled by its crew in 1905 after Japan's victory in the Battle of Tsushima - a key moment of the Russo-Japanese War.
Ever since, rumours have persisted that the ship was carrying 200 tonnes of gold for Russia's Pacific Fleet, to pay crew salaries and docking fees.
If true, the gold on board would be worth billions of dollars today.
Experts have raised doubts that Russia would ever have put that much gold on a single vessel, when it could have carried the precious cargo more safely by rail to its eastern port of Vladivostok.
According to South Korean news agency Yonhap, Shinil's announcement was soon followed by suspicions it might be running a scam.
The firm has faced allegations of trying to artificially boost share prices, or seduce investors into buying a crypto-currency issued by a Singaporean company, also named Shinil Group.
Choi Yong-seok, CEO of the South Korean company, has insisted the two firms are unconnected - though their founders are siblings, AFP reports.
South Korean media report that the Shinil Group based there was formed just before the ship find was announced, and was running on a very small capital base - not even enough to apply for salvage rights, which are 10% of a find's estimated value.
Yonhap reports that the ship's alleged treasure was initially claimed to be worth 130tr won ($116bn, £89bn) but in subsequent documents for the excavation approval, the value was lowered to 1.2bn won.