Before launching a full-scale attack against North Korea or a surgical strike against key targets, the United States would first have to consider evacuating American citizens and alerting its allies for fear of North Korean counterattacks, USA officials and experts said.
Neither Tillerson nor Mattis responded directly to strategist Steve Bannon's argument in an interview published Wednesday that there's no military solution to the North Korean threat.
A joint statement released after the meeting highlighted a strong condemnation of North Korea's "recurring provocations", which they noted had "entered a new phase" this year.
North Korea has in the past fired missiles and taken other steps in response to US and South Korean exercises.
US President Donald Trump warned North Korea last week it would face "fire and fury" if it threatened the United States, prompting North Korea to say it was considering plans to fire missiles toward Guam.
Tillerson warned that the USA will honor treaty obligations to defend Japan "without reservation", and would be working to improve military alliances with other countries in the region, including South Korea, India and Australia.
"But should different circumstances occur, then we will solidify the relation that we have with the USA with close communication".
"First, we simply do not have a comprehensive or precise picture of the North Korean nuclear programme, especially when it comes to the number of weapons and delivery vehicles - we do not know for sure where they are located or how well they are protected", a 2016 Stratfor report said.
"So, our effort is to cause them (North Korean regime) to want to engage in talks, but engage in talks with an understanding that these talks will lead to a different conclusion than talks of the past".
But, knowing that North Korea sits with a significant capability already within their grasp, I think it is only prudent that they fully understand the consequences, should they make a bad choice for themselves.
Tillerson added: "That is not our preferred path".
The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday. It is also advancing on their efforts to launch ICBM-class ballistic missiles, miniaturising nuclear weapons to warheads.
The top United States diplomat laid out the worldwide "peaceful pressure" campaign he is leading against the Democratic People's Republic of Korea, or DPRK, but in response to a question from CNN's Elise Labott, he added that the diplomatic approach "has to be backed with military threat" if North Korea chooses to move forward with destabilizing actions.
Thursday's meeting focused on a range of regional issues, including ongoing tensions with North Korea, and the future of the U.S. -Japan alliance and defense cooperation.
The statement additionally "called on the worldwide community to comprehensively and thoroughly implement the United Nations Security Council resolutions including the newly adopted Resolution 2371".
Kono called on the North's traditional ally and main trading partner, China, to take actions "to make North Korea change its behavior".
"We are accelerating implementation of the 2015 guidelines for US-Japan defence cooperation and continuing to realign US forces in Japan and Guam".
The ministers also vowed to advance trilateral and multilateral security cooperation with other partners in the Asia-Pacific region - notably South Korea, Australia, India and Southeast Asian countries - with the US committing to maintain a strong presence in the region.
Referring to trilateral security cooperation with South Korea, the joint statement stressed the need to enhance information-sharing and expand three-way exercises including missile warning, anti-submarine warfare and maritime interdiction operations. "Any initiation of hostilities will be met with an effective and overwhelming response".