"Armed soldiers are on board the boat," which has docked in Puerto Williams, on Chile's extreme southern tip, Rune Olsgaard told AFP in Oslo, adding: "Chilean authorities will decide how to proceed in this case this afternoon, Chilean time, at the earliest."
After slipping away from New Zealand authorities who wanted to block him from returning to the Ross Sea, Andhøy and four other men headed back towards Antarctica in late January without authorisation to discover the fate of comrades who were lost in a first unauthorised expedition headed by Andhøy last year.
In February 2011 he and a companion had tried to reach the South Pole on quadbikes as three others waited for them aboard their sailboat Berserk.
But the vessel disappeared when a fierce storm packing winds of 180 kilometres per hour battered the Ross Sea and the three on board were never found despite an extensive search coordinated from New Zealand.
Andhoøy was airlifted unharmed from Antarctica along with his companion after the first expedition but New Zealand authorities decided he should not be allowed to return after the massive resources they had deployed.
He also lacked the necessary authorisation from Norway's Polar Institute, which regulates Norwegian expeditions to the continent and runs a research station in Queen Maud Land.
The second expedition launched in January failed to locate Berserk, but Andhøy told the Dagbladet daily last week that he was considering a third trip to Antarctica to continue the search.
It was not clear why the Chilean navy had intercepted the boat, but Olsgaard said it appeared to relate to a "misunderstanding" with Wellington concerning a New Zealand national accompanying Andhowy, Busby Nobel.
According to New Zealand media, Nobel had been onboard the yacht in an Auckland port and had become part of the expedition against his will when Andhøy took off at full speed to skirt authorities.
But Olsgaard said Nobel had called the New Zealand consulate in Santiago to say he was on the ship of his own free will.
The Chilean coast guard has also accused Andhøy of being in Chilean waters with a boat sailing under a false name, but Olsgaard insisted the Russian-registered yacht Nilaya had been officially rebaptised Berserk in honour of the misfortuned ship lost during the first expedition.
The Norwegian foreign ministry meanwhile confirmed that it had been informed that Andhøy's boat had been rerouted to a Chilean port, but said it was not aware of any request from the Norwegian adventurer for consular assistance.