"North Korea has accelerated the threat that it poses to its neighbors and the world through its illegal and unnecessary missile and nuclear weapons programs", said Mattis at the conference, via Reuters.
"They must realise how serious the situation is". But this wouldn't be the first time the US sent its deadly warplanes toward the Korean peninsula to convey a message to the family of North Korean leader Kim Jong Un, who succeeded his father in 2014.
"I have never heard of this type of training exercises before in North Korea, but am not surprised", Chun In-Bum, a recently retired South Korean three star lieutenant general, told NK News.
It was also joined by PACOM Commander Harry B. Harris, US Forces Korea Commander Gen. Vincent K. Brooks and US Forces Japan Commander Lt. Gen. -South Korean military and diplomatic collaboration had taken on "a new urgency".
Trump has said, "all options are on the table" in dealing with North Korea, which has test-fired ballistic missiles, some of which have flown over Japan, and has repeatedly undertaken nuclear tests.
Mattis, however, also said recently that the US would seek "peaceful resolution" to the conflict with North Korea and had no intention of "rushing to war" with the nation.
Gen. Joseph F. Dunford, chairman of the US Joint Chiefs of Staff, hosted a trilateral meeting with his South Korean and Japanese counterparts - Gen. Jeong Kyeong-doo and Adm. Katsutoshi Kawano - in Hawaii on Sunday (local time).
Defectors have spoken of frequent air raid drills during times of tension in North Korea but not in recent years.
According to NK News, "daily air raid drills" were common in 1994 when the North and the US were "on the brink of war".
In a statement carried by the country's official Korean Central News Agency, the committee claimed that in campaigning ahead of the October 22 election, Abe's Liberal Democratic Party "kicked up a hysteric anti-(Pyongyang) racket, noisily trumpeting about the story of nuclear threat from the north and solution to the abduction of Japanese". "In this day and age of precision bombing and all-weather capabilities, [such] North Korean civil exercises either come from ignorance of modern war or just a propaganda campaign to frighten their own people and induce obedience".