Moscow - An American student was found dead in a mountainous region of Siberia on Monday a week after he disappeared in mysterious circumstances, Russian investigators said.
Colin Madsen, 25, disappeared in the mainly Buddhist Buryatia region of eastern Siberia after apparently walking out at night without a coat, prompting a massive search amid snowy and windy weather.
Madsen's body was found one and a half kilometres (a mile) from where he was staying in a village at the foot of the Sayan Mountains, located west of Lake Baikal, the Investigative Committee, which probes serious incidents, said.
A US embassy spokesman in Moscow told AFP: "We are aware of these reports and have been working closely with Russian authorities on the matter."
"I can confirm that Embassy consular officials are in the region to provide consular assistance," the spokesman added.
Investigators did not comment on the cause of Madsen's death, saying only that his body had no visible signs of injury and his wallet and ID documents had not been stolen.
According to police and investigators, Madsen walked out of the house where he was staying with friends between 2 and 5am on March 27, wearing only a T-shirt and trousers, hours before they were due to set off on a hike.
His friends spent the day searching for him before reporting him missing to police in the evening.
Investigators said they need to establish "why the lightly dressed student left the guest house without warning his friends and walked into the forest."
A post-mortem will look to see whether Madsen had traces of alcohol or drugs in his blood, investigators said.
The group of friends - two Americans and two Russians - "had used a drug" the day before Madsen disappeared, the investigators said without giving any details.
The group had not drunk alcohol together and had not quarrelled, investigators said.
Madsen, who originated from Jefferson City, Missouri, had been studying in the Siberian city of Irkutsk at the local branch of Moscow State Linguistic University since 2013. He spoke fluent Russian and had previously visited the area where he died four times.