A senior official at the U.S. Defense Department says an American missile defense system will be able to guard all of the United States by the end of the year from a possible North Korean missile attack.

Air Force Lt. Gen. Ron Kadish, director of the Missile Defense Agency, told reporters Wednesday that a decision on when to put the first stationary missile interceptors on alert has not been made, but that plans call for several to be operational by September.

The official said that by the end of the year, close to 10 interceptors are expected to be on alert at Air Force bases in Alaska and California. He said the interceptors will be linked to a specialized radar able to track inbound missiles over the Pacific Ocean.