The Flint Journal, Jake May
Ray Bishop, 41, paints in stenciled "USA" lettering onto Detroit Red Wings goalie Jimmy Howard's mask for the 2014 Olympics at his paint shop Tuesday, Jan. 28, 2014 in Grand Blanc Township, Mich.

WASHINGTON — A top U.S. intelligence official says there has been an uptick in reports of security threats against the Olympic Games in Sochi, but the key concern for an attack centers on locations outside the main event areas.

The director of the National Counterterrorism Center, Matthew Olsen, tells the Senate Intelligence Committee that there is "substantial potential" for a terrorist attack against so-called softer targets outside Sochi. He says there is extensive security at the sports venues in the Russian city.

FBI Director James Comey told the panel that U.S. cooperation with the Russian Security Service, the FSB, has improved and officials from the two agencies have discussed the Sochi threat.

Russia is mounting a massive security operation for the Olympics amid threats from Muslim insurgents from the Caucasus region.