Three climbers from Britain and Australia told Reuters on Tuesday that on September 30 they watched Chinese border guards aim their guns at a group of up to 30 people as they prepared to cross an icy pass from Chinese territory into Nepal.
Overseas Tibetan refugee groups, as well as the London-based International Campaign for Tibet, said a young Tibetan nun was killed in the incident, and a young boy may also have died.
The official Xinhua news agency said on Thursday that the people were attempting to cross illegally from Tibet into Nepal when a squad of Chinese border guards discovered them.
The troops tried to persuade the people to return home, but they "refused and attacked the soldiers", the report said, citing an unnamed Chinese official. "The frontier soldiers were forced to defend themselves and injured two."
One of the injured died later in hospital "due to oxygen shortage", the report said. Another was still in hospital.
Xinhua did not say whether the civilians carried guns or other weapons.
This first official Chinese confirmation of the border incident appeared hours after a foreign ministry spokesman said he could not verify foreign news reports of a border incident in the Himalayas.
"I've seen the reports about this, but I've no knowledge of the specific situation," Liu Jianchao, a ministry spokesman, told a news conference in Beijing.
Hundreds of Tibetans cross the Himalayas to Nepal every year, many making their way to a northern town in India, where their exiled leader, the Dalai Lama, has been living since 1959 after an abortive uprising against Chinese rule.
Nepal is home to more than 20,000 Tibetan refugees, but recent arrivals have not been allowed to stay and have had to travel on to neighbouring India.