A senior US security official said that airlines had been warned to watch for explosive materials that could be turned into a bomb on board a plane or on arrival in Russia.
The information has been passed to airports and some airlines that haver direct flights to Russia, including some operating from the United States, it was reported.
The security official did not say if any specific intelligence had led to the warning.
However, Dmitry Kozak, Russia’s deputy foreign minister, has said that the “level of threat in Sochi is no worse than in New York, Washington or Boston.”
Russian forces are on high alert to head off possible militant attacks at the Winter Olympics. The opening ceremony for the games takes place on Friday, though some events began on Thursday.
Meanwhile, two British snowboarders passed through qualifying rounds on Thursday. Jamie Nicholls made it to the Men’s Slopestyle final, and Billy Morgan (pictured below)is through to the semi-finals.