Media playback is unsupported on your device Media caption Greg Brooks: "It is the biggest shipwreck anyone has ever dreamt about"

A Maine treasure hunter says he has discovered a WWII-era shipwreck filled with platinum, now worth $3bn (£1.9bn).

Greg Brooks of Sub Sea Research says a wreck sitting 50 miles (80km) off the US Atlantic coast is the SS Port Nicholson, sunk in 1942.

The Port Nicholson, a British merchant ship, was torpedoed by a German U-boat in an attack that killed six people.

Some have expressed doubts the wreck holds platinum, and maritime law would complicate ownership claims.

Anthony Shusta, an attorney representing the British government, says it is unclear if the ship ever carried platinum.

"We're still researching what was on the vessel," Mr Shusta told the Associated Press news agency. "Our initial research indicated it was mostly machinery and military stores."

The United Kingdom will wait until salvage operations begin before deciding whether to file a claim on the cargo, he added.

'I'm getting it'

Mr Brooks says a US Treasury Department ledger shows platinum bars were on board, as part of a payment from the Soviet Union to the US for war supplies.

He also has underwater video footage he says shows a platinum bar surrounded by 30 boxes that he believes holds platinum ingots.

He has not yet brought up any platinum but says he and his crew hope to begin raising the treasure later this month.

"I'm going to get it, one way or another, even if I have to lift the ship out of the water," he said.

The treasure hunter said he held off the announcement of his find for four years while he negotiated salvage rights. Ownership rights are still unsettled.