South Korea's Defense Ministry also confirmed on Thursday that the US and South Korean Air Forces are conducting an annual training exercise - codenamed Max Thunder - until April 28.
Such a contingency could include the risk of an armed conflict breaking out as tensions on the peninsula have risen in the wake of multiple North Korean missile tests.
When asked by CBS News if she considers ballistic missile tests to be a provocation, Haley said Wednesday the USA evaluates North Korean action based on whether the country "violates Security Council resolutions, so they definitely have done that".
"They don't produce enough food to feed themselves".
North Korean state media has warned Washington of a "super-mighty pre-emptive strike" which would "reduce the U.S. to ashes".
It's a salient issue this week, after Vice President Mike Pence visited South Korea and threatened a military response to the regime of North Korean dictator Kim Jong-un unless the country abandons its pursuit of nuclear weapons.
Trump to visit Philippines, Vietnam in November for regional summits: Pence
Moreover, Trump would be gracing the event, European PPP Expertise Centre alias EPEC Summit scheduled to be held in Vietnam. This will be President Widodo's second time to visit the Philippines as head of his country.
North Korea has accelerated its nuclear and missile tests in recent years, despite worldwide condemnation and United Nations sanctions.
North Korea's leader Kim Jong-un waves at a performance on Sunday.
He said that an "all-out war" would result if the United States took military action.
The unannounced visit at the start of Pence's 10-day trip to Asia was a USA show of force that allowed him to gaze at North Korean soldiers from afar and stare directly across a border marked by razor wire.
"I would see such an action as escalatory, but I couldn't guess how Kim Jong-un would interpret it", the report quoted Abraham Denmark, a senior official in Barack Obama's administration, as saying.
The moves are said to be part of an effort to "reduce the time to react to a North Korea contingency".
An official Chinese newspaper said on Friday there was optimism about persuading the North to end its pursuit of a nuclear programme without the use of force, "now that even the once tough-talking Donald Trump is onboard for a peaceful solution".
After Xi's return to China, Trump continued to pressure him.