The three ministers recognized that the United States, South Korea and Japan face common security challenges in the Asia-Pacific region, and declared that North Korea's development of nuclear and ballistic missile capabilities - including its intercontinental ballistic missile - threatens the security and prosperity of the three nations, according to the statement.
South Korean Defense Minister Song Young-moo prepared Monday for a round of bilateral and multilateral diplomacy in Clark, the Philippines, on North Korea and other regional security issues.
He added: "The threat posed by North Korea has grown to the unprecedented, critical and imminent level". South Korea's defense minister, Song, said that North Korea's behavior is "becoming worse and worse".
North Korea watchers say the North's leader may plan to declare the completion of the reclusive nation's nuclear weapon and ICBM development in his New Year's address on January 1, 2018.
USA is eager to emphasize diplomatic efforts to resolve the crisis peacefully as escalating tension between Washington and Pyongyang stoked fears of "armed confrontation".
Washington D.C. [U.S.A.], October 23: Japan's Defence Minister Itsunori Onodera on Monday reportedly said that the threat from North Korea is both unprecedented and imminent.
Trump has been locked in a war of words with North Korean leader Kim Jong Un, calling him a "rocket man" on a suicide mission for openly pursuing a nuclear-tipped missile capable of hitting the United States. "The country has steadfastly improved it nuclear and missiles capability", said Onodera.
Defense ministers from the Association of Southeast Asian Nations (ASEAN), in a joint statement, underscored the "need to maintain peace and stability in the region" and called "for the exercise of self-restraint and the resumption of dialogue to de-escalate tensions in the Korean Peninsula".
Mattis's visit to Seoul comes ahead of Trump's first presidential trip to Asia next month, which also includes South Korea. Many experts believe those missiles - which North Korea has tested by firing over Japan - could reach the U.S. mainland.
The comments from Mr Onodera came amid escalating tension between North Korea and the West.
They also vowed to work together to combat terrorism as they condemned the attack by the Maute militant group in the southern Philippine city of Marawi.
The Philippine military said on Sunday that its troops were battling a final group of about 30 pro-Islamic State group terrorists as a almost five-month siege neared its end in Marawai.
On Thursday, Mattis will lead the US delegation in Thailand for the cremation rites for the late King Bhumibol Adulyadej.