Bernanke was asked at his news conference whether the flare-up in Cyprus signals that the U.S. financial system might be more vulnerable than bank "stress tests" have shown.

NPR: Fed Stands By Stimulus, Sees Stronger US Economy

Officials said earlier Thursday that one of the U.S. planes fired a flare to ward off the Iranian fighter, but later said no flare had been fired.

WSJ: U.S. Fighters Warned Off Iranian Jet

The latest flare-up in the bilateral relationship comes as the U.S. is withdrawing its forces and negotiating with Mr. Karzai what American military presence, if any, will remain in Afghanistan after the coalition's mandate ends next year.

WSJ: Karzai Provokes Pushback at Home