United States Secretary of State Rex Tillerson arrives in Tokyo today for a four-day tour of North-east Asia, as fears of a nuclear stand-off loom large, with North Korea said to be gearing up for its biggest test yet.
The trip, which includes stops in Seoul and Beijing, will be closely watched for clues on how the Trump administration will tackle its first major foreign policy crisis. It is aimed at reassuring key defence allies Japan and South Korea, while fostering dialogue with China.
A US State Department official said North Korea is at the top of the agenda. "We will defend our friends and allies, South Korea and Japan, and we will seek to work collaboratively to the maximum extent possible with important partners such as China."
Experts said Mr Tillerson will cajole Tokyo and Seoul, whose ties are shaky over unresolved "comfort women" issues, to work together.
He will also try to mollify Beijing over the deployment of the US Terminal High Altitude Area Defence (Thaad) anti-missile system in South Korea.
Keio University's Associate Professor Ken Jimbo said: "The US is considering a wide range of policy alternatives to North Korea, and Mr Tillerson will need to take regional perspectives into his account."
In Tokyo, Mr Tillerson will meet Prime Minister Shinzo Abe and Foreign Minister Fumio Kishida, with whom Dr Jeffrey Kingston of Temple University Tokyo thinks the possibility of Thaad deployment in Japan will be discussed.
Dr Koichi Nakano of Sophia University said there might also be talks on "Japan exercising collective self-defence upon the US request, most notably in South China Sea patrol missions" to curb Chinese assertiveness in the waterway.
In Seoul on Friday, he will meet Acting President Hwang Kyo Ahn and Foreign Minister Yun Byung Se.
South Korea, which ousted its president Park Geun Hye last week, must hold presidential elections by May 9.
There are "no plans" for Mr Tillerson to meet political opposition, the US official said. This includes liberal presidential front runner Moon Jae In, who opposes an intelligence-sharing pact with Tokyo and the deployment of Thaad.
In Beijing on Saturday, Mr Tillerson will meet Foreign Minister Wang Yi, State Councillor Yang Jiechi and, possibly, both President Xi Jinping and Premier Li Keqiang.
Chinese analysts see a lot of misunderstanding over North Korea and the South China Sea between the two sides.
International relations professor Su Hao of the China Foreign Affairs University said: "There can be a mutually beneficial relationship but for this to happen, both sides have to sit down, have a frank discussion and forge understanding."
Still, experts note that Mr Tillerson is hamstrung by the fact that senior policymaker roles in the State Department remain unfilled.
Dr Go Myong Hyun of South Korean think-tank Asan Institute of Policy Studies said: "He is not in a position to formulate any big picture or change in approach towards North Korea and China at this point."
•Additional reporting by Chang May Choon in Seoul and Lim Yan Liang in Beijing