Washington, DC (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 on Wednesday 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.
Russian transportation officials this week banned liquids in airline carry-on luggage, according to a report from the Russian news agency RIA Novosti.
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."
Secretary of State John Kerry, in an exclusive interview with CNN's "The Lead with Jake Tapper," said on Wednesday that that "anybody who wants to go to the Olympics, which are just a great event, should go. And we're not telling people not to go."
Kerry, whose comments aired before news of the toothpaste advisory broke, added that people should be alert and take precautions, advice he says has been requisite since the 9/11 attacks.
"We've got a new consciousness about this," he said.
Terrorism experts say that airlines continue to be a target of terrorists wishing to make a spectacular impact with an attack. The focus since 2001 has shifted from hijackings to bombs, especially those that might be hidden in luggage.
U.S. authorities are also mindful of creative package or other novel ways to conceal explosives. For instance, a failed attempt to blow up an overseas flight heading to Detroit on Christmas Day in 2009 involved a bomb concealed in a passenger's underwear.
Shortly after 9/11 a man was convicted of trying to blow up a transatlantic flight with explosives hidden in his shoes.
CNN's Jim Acosta and Jake Tapper contributed to this report