China has agreed reluctantly to U.N. Security Council resolutions sanctioning North Korea, but is adamantly opposed to measures that might bring about a collapse of North Korean leader Kim Jong Un's regime.
This means the Trump administration actually has room to explore options short of military action and the apparent red line of "It won't happen!"
Joseph Yun, US special representative for North Korea policy, arrived in Seoul later in the day after visiting Beijing over the weekend to meet with his Chinese counterpart Wu Dawei.
After that launch, South Korean defence officials said that the Unha rocket used in the launch, if successfully reconfigured as a missile, could fly more than 12,000km with a warhead of 500 to 600kg - far enough to reach most of the US.
Davis added that reports of the test "would be consistent with the pattern we've seen with North Korea to continue to develop its ballistic missile program, and it's a program that we have concerns with".
South Korea's military acknowledged Monday that the test, which apparently was conducted on Saturday, showed the North was developing a more sophisticated engine. That would put parts of the United States in range.
Sunday's test was a "precisely-timed spectacular", said Peter Hayes, director of the US-based Nautilus Institute, "the kind we've come to expect from Kim Jong Un". The North's "Dear Leader", Kim Jong-un, said the test was a "great, revolutionary victory" for the country and its space program.
South Korean daily Chosun Ilbo also cited an unnamed source who said Han had likely provided North Korean authorities with information on Jong Nam's travel plans to Malaysia.
It launched its latest satellite - the Kwangmyongsong 4, or Brilliant Star 4 - into orbit on February 7 past year, just one month after conducting what it claims was its first test of a hydrogen bomb.
North Korea operates on a military-first principle, which Kim has increasingly shifted towards nuclear and weapons technology, and away from the traditional standing army.
The top U.S. diplomat indicated a need for tougher UN Security Council sanctions on North Korea's nuclear programme and other weapons of mass destruction.
Moreover, the newly tested engine apparatus appears to be too large to fit into any of North Korea's known ICBM prototypes, he added.
In South Korea, he outlined a tougher strategy to confront North Korea's nuclear threat. The engine tested in September included no visible steering mechanism, leading us to speculate that perhaps North Korea was planning to swivel the entire engine on gimbals.