Russian authorities have detained an American and a British citizen in the far east after the pair made a rare crossing by foot of a frozen 56-mile stretch of the Bering Strait, officials said Tuesday.

The two were arrested in Chukotka province for failing to register with the authorities, Andrei Orlov, spokesman for the Federal Security Service's (FSB) northeastern border guard division, said on NTV television. All visitors are required to register with police within three days of their arrival in Russia, even if they have visas.

Russian authorities did not identify the two or say when they were arrested.

But one of the adventurers, Briton Karl Bushby, said on his Web site that he and Dimitry Kieffer of Anchorage, Alaska, reached Chukotka province Friday. It took them 15 days to walk the 56 miles from Alaska to Russian territory.

The Web site said Bushby, a 36-year-old former paratrooper, made the crossing as part of a round-the-world walk that began in 1998 at the southern tip of South America.

Bushby's father, Keith, of Hereford, England, confirmed the two had arrived in Russia on Friday and had been detained sometime after that, though he did not know exactly when.

In a posting dated Friday, March 31, Karl Bushby's Web site said he and Kieffer were in the village of Uelen, near the point where the Bering Sea meets the Chukchi Sea, about 560 miles northwest of the provincial capital Anadyr.

Keith Bushby said the travelers were headed south down the coast en route to the city of Provideniya, about 380 miles northeast of Anadyr, to officially register with Russian authorities. But they were stopped on their way there in the small village of Lavrenty, about 500 miles northwest of Anadyr.

They did not enter the country at a border crossing, so they had no stamps in their passports.

"Because they were walking across the Bering Strait, they could not take the normal route. Consequently, they didn't have the correct stamps and a landing permit," Keith Bushby told The Associated Press.

"We don't blame the Russian bodyguards because they are doing their job. Karl fully expected a problem, because he knew this would happen."

He added that his son was feeling fine but was upset that his trip through Russia could be cut short if the authorities deny him permission to continue his travels.

"He will be worried that the authorities will not let him walk any further in Russia," Keith Bushby said.

Orlov said the detained men had Russian business visas but failed to complete registration procedures as foreigners are required to do. The pair also had satellite phones, GPS mapping equipment, a video camera and a pistol, he said.

"So far, the actions of these tourists is unclear, so to speak, and an investigation is being conducted," Orlov said.

The ITAR-Tass news agency quoted FSB spokesman Vadim Shibayev as saying the two were accused of illegal border crossing and are currently being questioned by authorities.

"The American and the Briton did not notify the Russian side through official channels of their (border) crossing, which not only violated border legislation, but also put their lives in serious danger," Shibayev was quoted as saying.

The U.S. Embassy said its consulate in the Russian Pacific port of Vladivostok was handling the incident, but it could not confirm the identities of the travelers.

Staff at the British Embassy said they were aware of media reports and were getting in touch with Russian authorities in Chukotka but could not verify the information or provide more details.

Bushby wants to be the first person to walk all the way around the world, his Web site says. Since the beginning of his journey on Nov. 1, 1998, he has covered 17,000 miles, walking through South, Central and North America.