SHARECOMMENTMORE

(CBSNews.com) - 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.

The United States is sending 230 athletes accompanied by a coaching and support staff of 270. As many as 10,000 Americans are expected to attend as spectators, though in recent days some participants have urged relatives to stay away because of security threats.

The senior officials say there has been an uptick in the number of threats in recent weeks, though they also note that an increase before a major international event is not unusual. The U.S. will monitor threats throughout the games.

Russian authorities have been searching in particular for a woman identified as Ruzana Ibragimova, who has pledged to revenge the death of her husband, an Islamic militant killed last year by Russian security forces.

crop.grab.blackwidow02.jpg
Russian authorities have put out an alert for this woman, Ruzana Ibragimova.
CBS NEWS

Police have been distributing posters of Ibragimova and visiting hotels. They are also worried that other widows of men killed by security forces will try to carry out attacks, possibly suicide attacks.

Ryan Suter, a star defense man for the NHL's Minnesota Wild who will play for Team USA, said hewants his wife, his two children and his parents to stay away.

"It's definitely a concern," he said. "I look forward to going to the Olympics and being part of it. You hear all these stories about different things; it's definitely a concern."

His Minnesota teammate, Zach Parise, has also told his family to skip Sochi.

"I mean it's nerve-wracking, that's for sure," Parise said. "When you see that stuff going on, it's not very comforting."

The U.S. government will have consular officials on the ground in Sochi and Americans are being encouraged to record their visit in a State Department program called the Smart Traveler Enrollment Program or STEP.

Opening ceremonies are to take place on Feb. 7.

Ralph Lauren Corp. unveiled the American official uniform on Thursday. The red, white and blue uniforms include stars, stripes, the American flag and the Olympic rings.

© 2014 CBS Interactive Inc. All Rights Reserved.