U.S. Olympic athletes warned against wearing Ugly Sweaters.... I mean, uniforms outside venues in Sochi

U.S. Olympic athletes are being warned not to wear their uniforms outside the games venues in Sochi because of fears of terrorist attacks in the southern Russian city, according to senior officials in the Obama administration.

The unusual caution comes as Russian security forces search for a so-called "black widow" who they fear may be plotting to carry out an attack at the upcoming Winter Olympics. Athletes participating in earlier games, including London and Beijing, did not face a similar warning.

The United States will have a large security contingent at the games – including FBI personal and diplomatic agents. Officials will be prepared for evacuations by air or sea if needed, the senior officials said, with ships being sent to the Black Sea.