Gibraltar has impounded a Russian billionaire's superyacht - one of the world's biggest - because the German shipbuilder says he still owes 15.3m euros in fees, BBC reports.

The claim has kept Andrei Melnichenko's Sailing Yacht A stuck in Gibraltar, a British territory, since Wednesday.

The Bermuda-registered vessel, built by Nobiskrug, left the Kiel shipyard in northern Germany two weeks ago.

It is 143m long and has three masts, the main one 100m high.

The superyacht, boasting a gross tonnage of 12,600, is reported to have cost at least €400m. Nobiskrug says it has an underwater observation pod, hybrid diesel-electric propulsion and "state-of-the-art" navigation systems. It was designed by Philippe Starck.