HOUSTON -

Just hours before the start of the 2014 Winter Olympics in Sochi, the Department of Homeland Security has issued a warning for airlines flying to Russia.

Airlines around the world received the advisory Wednesday, warning of potential explosives in toothpaste tubes.

Richard Stoll, a professor of political science at Rice University, said the government doesn't often issue these specific kinds of warnings.

"This suggests to me that there was something specific," said Stoll. "There was some communication that was picked up that mentioned toothpaste bombs or some person that was being tracked that mentioned something about it, at least in a vague way."

A government source told CNN that the information was from a credible source, and that government officials are taking the situation very seriously.

"I think it's not that likely, but of course we have seen terrorist attacks at the Olympics before: Munich in '72 and of course Atlanta in '96," said Stoll.

But Secretary of State John Kerry doesn't want the advisory to keep people from traveling to the games.

"I believe that anybody who wants to go to the Olympics, which are just a great event, should go," Kerry said. "We're not telling people not to go."

The Department of Homeland Security did not reveal either the source of the intelligence or the time frame involved.