The U.S. and U.K. have imposed a new round of sanctions on Iran as concern grows that Tehran's unprecedented attack on Israel could fuel a wider war in the Middle East.

The sanctions are meant to hold Iran accountable for its weekend attack and to deter further such activity. But the practical impact is likely to be limited because many of the targeted companies already were subject to U.S. sanctions and the individuals singled out for new sanctions are unlikely to have assets in U.S. jurisdictions.