North Korea is working to develop a nuclear missile that can strike the United States.
A top-ranking USA military official on the Korean peninsula said the biggest concern is that North Korean leader Kim Jong Un will "miscalculate" his chances of winning any military fight against the US and its ally, South Korea.
In his ABC interview, McMaster said that Trump had directed U.S. military, diplomatic and intelligence officials to provide him with options - in concertation with regional allies including China - that could be used "if the North Korea regime refuses to denuclearize". "We stand alongside our worldwide partners in making clear that North Korea must adhere to United Nations resolutions created to secure peace and stability in the region and stop its pursuit of nuclear weapons", he said. His trip to the region comes amid growing tensions between the US and North Korea.
A White House foreign policy adviser told reporters aboard Air Force Two that the type of missile that North Korea tried to fire on Sunday was medium-range, and that it exploded about 4 to 5 seconds after it was launched.
Right after touching down at a US air base in Pyeongtaek, 70 kilometers south of Seoul, Pence visited South Korea's national cemetery in Seoul, a symbolic gesture to highlight the alliance forged during the 1950-53 Korean War.
"We will see what happens!"
He said: "We would sneak into the South, change our clothing, go into areas where there are lots of foreigners and capture some of them".
According to the adviser, the test had been expected and the USA had good intelligence both before and after the launch.
Mr Pence is due in Seoul at the start of a 10-day trip to Asia in what his aides said was a sign of the U.S. commitment to its ally in the face of rising tension over North Korea.More news: Modi Confident on Teesta, Bangladesh Extended $5-bn Credit Lines
Trump has projected a transactional attitude toward China, saying in interviews and remarks that he planned to use trade as a negotiating tool for Xi's cooperation on North Korea. She advised patience with China on the issue. At the same time, Vice President Mike Pence warned at the Korean Demilitarized Zone that America's "era of strategic patience is over".
Pence says, "North Korea would do well not to test his resolve".
North Korean state media has made no comment on the launch.
The missile launched earlier this month flew about 60 kilometres, but what United States officials said appeared to be a liquid-fuelled, extended-range Scud missile only travelled a fraction of its range before spinning out of control. "On the contrary, our economic presence in the region is enduring", the adviser said.
On State of the Union, Sen.
"The key, I think, to this situation - and I think President Trump understands this - is dealing with China", Sanders said.
"They can stop this if they want to due to their control over the North Korean economy", McCain said.
And I think there is global consensus now, including the Chinese, and the Chinese leadership, that this is a situation that just can't continue.
Information for this article was contributed by Ken Thomas of The Associated Press; by Julie Hirschfeld Davis of The New York Times; by Kanga Kong, Justin Sink, Jennifer Jacobs, Tsuyoshi Inajima and Michelle Jamrisko of Bloomberg News; and by Sean Sullivan of The Washington Post.