"We're going to consult with the Republic of Korea on North Korea's efforts to advance its ballistic missile and its nuclear program", a White House foreign policy adviser told reporters, previewing Pence's trip. "On North Korea, they worked together". He has repeatedly said if China, North Korea's dominant trading partner, is unwilling to do more to pressure the North, the USA might take the matter into its own hands.
Some analysts were puzzled by this.
Pence landed in South Korea hours after the North's failed missile launch. "They can stop this if they want to due to their control over the North Korean economy".
During a briefing with Gen. Vincent Brooks, head of U.S. Forces Korea, Pence said the alliance between Americans and South Koreans "is historic" and "a testament to the unshakeable bond between our people". "Even failed launches tell them something and improve their programme", Thornberry told Fox News Sunday.
Trump himself asserted on Sunday that China was working with the United States on "the North Korea problem".
After stopping in Seoul, Pence is to travel to Tokyo; Jakarta, Indonesia; and Sydney.
Osan Air Base is just 48 miles from the border with North Korea, and its air operations center tracks airspace over all of South Korea.
China reiterated on Monday its opposition to the deployment of a sophisticated US anti-missile system in South Korea.
South Korea made this decision last July after much equivocation.
Pyongyang insists it needs a powerful arsenal - including atomic weapons - to protect itself from what it says is the ever-present threat of invasion by hostile USA forces.
The U.S. air base's biggest tool in defense is the patriot missile, created to detect and stop a wide range of attacks - including from inbound ballistic missiles - with almost 100 percent accuracy, the military claims. "The United States wants to project a more muscular image when it comes to the policy so some unpredictability serves that cause".
"It's a critical point for the defense of South Korea in recognizing it's not an offensive weapon".
Pence will land in Seoul the day after North Korea's biggest national day, the "Day of the Sun".
The complicating factor here is China. North Korea is thought to have a small arsenal of atomic bombs and an impressive array of short- and medium-range missiles.
Although Trump met with Chinese President Xi Jinping earlier this month to discuss the increasingly hostile state, he tweeted last week that he discussed North Korea's recent missile launches last week.
China on Friday warned that "storm clouds" were gathering. For most young South Koreans, today was less about fear of war than about the tongue-in-cheek holiday "Black Day", an answer for singles to the important couples' holiday White Day, held a month earlier.
North Korea's vice foreign minister says the situation on the Korean Peninsula is now in a "vicious cycle".
The country launched a long-range rocket and conducted two nuclear tests past year, including its most powerful to date. The administration's immediate emphasis, the officials said, will be on increasing pressure on North Korea with the help of China.
Tensions are deepening as the US has sent an aircraft carrier to waters off the peninsula and is conducting its biggest-ever joint military exercises with South Korea. But at the same time, McMaster said on "This Week" on ABC, "it's time for us to undertake all actions we can, short of a military option, to try to resolve this peacefully". "But for this particular case, if they took the time and energy to launch a missile that failed, we don't need to expend any resources against that".
Tensions are expected to continue for several weeks at least.
He didn't respond to the missile firing but posted on Twitter Sunday morning: "Why would I call China a currency manipulator when they are working with us on the North Korean problem?"
Trump Advisers to Discuss Paris Agreement on Tuesday
Tuesday's meeting will mark the first time that senior advisers to the president have a formal discussion about Paris. The head of the Environmental Protection Agency has called for America to "exit" the Paris Climate Agreement.