The US has warned airlines with direct flights to Russia that explosives hidden in toothpaste tubes could be smuggled onto planes.The Department of Homeland Security's warning comes on the eve of the Winter Olympics' opening ceremony in the Russian Black Sea resort of Sochi.
It said it shared relevant information with partners at home and abroad "out of an abundance of caution".
But it was not aware of any specific danger to the US at this time.
Volgograd bombingsUnnamed security officials were quoted as saying there were fears toothpaste tubes could be used to smuggle explosives which could then be used to assemble a bomb either in flight or upon arrival at the Olympics.
The Department of Homeland Security said in a statement that although it is "not aware of a specific threat... this routine communication is an important part of our commitment to making sure we meet that priority".
The White House National Security Council said the latest threat had not altered existing travel guidelines for Sochi.
"If we should receive information in the coming days and weeks that changes our assessment of whether people should travel to Sochi, we will make that information public," spokeswoman Laura Magnuson told US media.
The US has also placed two warships in the Black Sea in case of a security breach during the games, scheduled for 7-23 February.
Fears were raised following two suicide attacks in Volgograd in December, and numerous threats from Islamist militants in the Caucasus region.
Two failed attempts have been made in recent years to detonate explosives on airliners.
Briton Richard Reid tried to set off a bomb packed in his shoes on a Miami-bound flight in 2001, while Nigerian Umar Farouk Abdulmutallab attempted to trigger explosives hidden in his underwear on a plane to Detroit in 2009.