(CNN) -- The United States is advising airlines with direct flights to Russia to be aware of the possibility that explosive materials could be concealed in toothpaste or cosmetic tubes, according to a law enforcement source.
The source emphasized that there was no known threat to the United States, but the notice to U.S. and international carriers is based on new intelligence information ahead of the start of the Olympics in Sochi this week.
"Out of an abundance of caution, (the Department of Homeland Security) regularly shares relevant information with domestic and international partners, including those associated with international events such as the Sochi Olympics," the agency said in a statement.
The Obama administration has not indicated it is not safe to travel to the Olympics.
"As we have said, 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 through the State Department's usual channels," a senior administration official said.
Matthew Olsen, a top U.S. counter-terrorism official, highlighted concern in testimony to Congress on Tuesday about whether Muslim fundamentalists in disputed regions of Russia -- or other groups -- could launch attacks on selected targets.
"There are a number of specific threats of varying degrees of credibility that we're tracking," he said. "And we're working very closely with the Russians and with other partners to monitor any threats we see and to disrupt those."