U.S. Defense Secretary James Mattis said that his responsibility is to have military options should they be needed.
 
Mattis made the remarks to reporters at an event in California on Thursday, adding that the U.S. prefers a diplomatic approach to the North Korean threat.
 
He said that the U.S. is dealing with the North Korean threat with an effective diplomatic effort. 

He warned that the tragedy of war is well known and a military conflict could be 'catastrophic.'