The actions have not gone unnoticed in North Korea, which has threatened the key US naval and air force bases on America's Pacific territory of Guam that houses about 160,000 people.
The U.S. nuclear-powered submarine MI approaches a naval base in Busan, South Korea.
Guam is a major military hub and home to US bombers that periodically fly missions over the divided Korean Peninsula.
After several days, North Korea appeared to back down from his threat, though.
North Korea renewed threats against the US territory of Guam as South Korea and the United States prepare for a joint naval exercise next week.
It is unlikely to have any effect on next week's planned major joint-navy drill between Sourth Korea and the U.S.
It remains unclear whether North Korea will lash out with a weapons test during the exercise, as it often has in the past.
North Korea is preparing to fire multiple short-range rockets around the opening of the Chinese Communist Party's twice-a-decade congress on 18 October, a South Korean daily newspaper reported Wednesday.
The drill, which involves the aircraft carrier Ronald Reagan, is scheduled to begin Monday in waters east and west of South Korea.
The researcher, Kim Kwang Hak, did not elaborate but recalled North Korea's August warning that it could launch missiles near Guam, home to the US air base from which the B-1B long-range bombers took off on Tuesday.
The maneuvers will take place in a time of high tension in the peninsula following the interaction of warmongering, some say, between the regime led by Kim Jong-un and Trump, who plans to visit the region between the 2nd and 14th of November.
These actions "reinforce our determination about the need to tame the United States with fire, and keep our hand closer to the trigger and be ready to take any countermeasures required", the commentary said.
North Korea has made similar threats against the United States for decades. Over 60 percent said they do have confidence in "top national security and diplomatic officials" to handle the situation.