MOSCOW — It is hard to imagine who was more stunned: the adventurers who crossed more than 50 miles of the Bering Strait's frigid, treacherous swells to Russia from Alaska in motorized water scooters last week, or the Russian border agents in an armored tank who watched them appear on shore, seemingly out of nowhere.

On Wednesday, the team of six men — shadowed by a Russian military helicopter — did an about-face and returned to the Alaskan coast after spending four days in detention in Lavrentiya, a remote village in the Chukotka region.

The six, led by Steven Moll, 41, of Folsom, Calif., had hoped that after reaching Chukotka in the Russian Far East, they could continue south for 5,000 more miles to Taiwan.

Each of the six rode a 2008 GTX, 215-horsepower Sea-Doo, made by the Canadian company Bombardier, that carried enough gasoline for a 250-mile trip. They had planned to buy more fuel at stops along Russia's vast eastern coast.

But what seemed like a well-scripted stunt hit a snag when the headlights from the watercraft sent Russian border agents into high alert. Much of the coastal region is designated as a prohibited military zone.

"The Russian guards were just as surprised as they were," said Chad Dalbec, the team's media manager, who received text messages and video updates from Moll during the detention.

"They saw the headlights from the Sea-Doo coming up on the beach, and then the tank rolled up with the border guards."

Although the team had proper visas to enter Russia, Moll said in a Twitter posting that he and his crew were fingerprinted and detained for four days because they had entered a military zone.

They were confined to a building resembling a gymnasium, he said, as the border guards shuttled paperwork to Moscow, eight time zones away, in a decidedly low-tech process Moll called "Third World," adding a colorful epithet.

In a video update Saturday on YouTube, Moll, wearing sunglasses and a baseball hat on a small village road, said the team was being treated well and had been taken to visit local museums. The Sea-Doos, which could be tracked from the United States by GPS, were being held under armed guard.

Chukotka has proved a formidable obstacle to would-be world travelers before.

In 2006 Karl Bushby, a Briton trying to circumnavigate the globe on foot, walked across the frozen Bering Strait into the region and was arrested for failing to register with the Russian authorities after coming ashore.

On Wednesday, after their expulsion from Russia, the team made a six-hour cannonball run back across the strait, whose waves can reach a height of 20 feet or more.

Motorized water scooters "are so small that you literally have to climb up the wave, break it and then coast down," Dalbec said. "It is definitely treacherous seas, and it has killed people before."

Moll said from Alaska that the team planned to travel around the state and through the Northwest Passage toward Iceland.

The team had tried to cross the strait in 2011 but abandoned the trip after one of the watercraft broke down.

This time, Moll said, after the Russians "got through all the paperwork, we shook hands, we said we're all friends, but we have to go home."