The United States is advising airlines with direct flights serving Russia to be aware of the possibility of explosive materials concealed in toothpaste or cosmetic tubes, CNN reports.

Rep. Michael McCaul, chairman of the House Homeland Security Committee, said the Department of Homeland Security issued a bulletin to airlines flying to Russia warning of the potential threat. The bulletin said that officials believed that the explosives might be used during flights or smuggled into the city of Sochi, where the Winter Olympics begins this week.

The article reports that authorities have increasing confidence about the safety of Sochi and the Olympic venues, but U.S. intelligence is picking up increasing chatter that causes worry about targets outside the Sochi area, including regional transportation links.