Russian border guards are holding an American man who came ashore in the remote far eastern Chukotka region after sailing in a dinghy from Alaska.
The man’s motives are not clear. He was found exhausted near Lavrentiya, a coastal village, Russian media report.
Russia’s foreign ministry named him as John Martin, born in 1972, from Anchorage. He reportedly got lost at sea after leaving the Yukon River.
At its closest point mainland Alaska is just 89km (55 miles) from Chukotka.
US diplomats are trying to resolve the case with Russian officials. Mr Martin is reported to be in good health now.
Russian Foreign Ministry spokeswoman Maria Zakharova said Mr Martin had “travelled down the Yukon River in Alaska in his personal one-seat boat.
“About two weeks ago, he decided to take to the open sea. Due to inclement weather and because he lacked navigation equipment, he spent several days in the open sea. This is how he ended up in the Russian Federation.”
She said Mr Martin received medical treatment in Lavrentiya and his condition was “satisfactory”. He will be transferred to Anadyr, Chukotka’s main town, she said.
Earlier, a source close to the investigation quoted the American as saying he had been fishing along the Alaskan coast and had decided to sail from the US to China, but ended up in Russia.
Chukotka’s proximity to Alaska made it a highly sensitive region during the Cold War.
It is Russia’s second-least populated region, with about 50,500 inhabitants, and its infrastructure is poor. Many rural inhabitants still rely on traditional hunting and reindeer-herding.