Foreign Office diplomats are trying to secure the release of an adventurer from Hull who is being held in Russia after creating an exploration record.
Ex-paratrooper Karl Bushby, 37, is the first Briton to walk across the Bering Strait, the treacherous 58-mile frozen sea between North America and Russia.
He spent 14 days walking on shifting plates of ice in temperatures of -30C, during a world trip lasting 12 years.
The Russian authorities are holding him for alleged paperwork irregularities.
A spokesman for the UK Foreign Office told BBC News they were in contact with the Russian authorities.
He added: "We are still trying to clarify the facts, but it seems he was lacking the correct border stamps.
"We hope this will be resolved quickly."
The adventurer began his mission in Chile in 1998 and is hoping to return to England by 2010.
The trip will take him across four continents, 25 countries, six deserts and seven mountain ranges.
The British explorer, formerly of Sutton Park in Hull, conquered the strait with temporary companion, Dimitri Kieffer, a French adventurer and specialist endurance racer, who has also been detained by the Russian authorities in Chukotka.
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