A woman passes by a TV screen showing a local news program reporting on North Korea's threats to strike Guam with missiles at the Seoul Train Station in Seoul, South Korea, Aug. 10, 2017.
A woman passes by a TV screen showing a local news program reporting on North Korea's threats to strike Guam with missiles at the Seoul Train Station in Seoul, South Korea, Aug. 10, 2017.

WASHINGTON - U.S. President Donald Trump stiffened his resolve against North Korea Thursday, saying that if Pyongyang initiates warfare “things will happen to them like they never thought possible.”

Trump said that his earlier warning to inflict “fire and fury” on the reclusive communist regime for its nuclear weapons development program perhaps “wasn’t tough enough.”

Asked what would be tougher, Trump told reporters at his golf resort in Bedminster, New Jersey, “You’ll see. ... North Korea better get their act together, or they’re going to be in trouble like few nations ever have been in trouble in this world.”

Watch: Trump Doubles Down on His Promise to Curb North Korea

Trump spoke hours after North Korea said it is finalizing a plan to launch a salvo of four ballistic missiles to the waters off the shores of the U.S. territory of Guam, Pyongyang’s latest provocation in the war of words between it and Washington.

Later Thursday at an event in California, Defense Secretary Jim Mattis said the United States is focused on diplomacy, but it is his responsibility to have military options ready “should they be needed” in the event of a war with North Korea — an option he said “would be catastrophic.”

Mattis stressed, however, that diplomatic efforts were gaining traction. “I want to stay right there, right now,” he added.

In an unusually detailed announcement, North Korea’s military said Thursday that within a week it would hand the regime’s leader, Kim Jong Un, a plan to fire Hwasong-12 missiles over Japan toward Guam, 3,300 kilometers to the south.

General Kim Rak Gyom, the commander of the North’s strategic rocket forces, told the state-run KCNA news agency the military would “wait for his order.”

North Korea’s state media has said that under the plan four intermediate-range missiles would be fired into waters 30-40 km (18-25 miles) from Guam “to signal a crucial warning to the United States.”

Guam residents said Friday they were anxious but overall “unworried” by missile threats from North Korea.

Friday, South Korea’s presidential office said that South Korea’s chief of national security, Chung Eui-Yong, and his U.S. counterpart H.R. McMaster reaffirmed their close cooperation on North Korean issues.

Chung and McMaster had a telephone conversation to discuss North Korea, presidential spokesman Park Su-hyun said.

Mixed signals

U.S. Ambassador to the United Nations Nikki Haley
FILE - U.S. Ambassador to the United Nations Nikki Haley speaks to reporters at U.N. headquarters after a Security Council vote on a new sanctions resolution that would increase economic pressure on North Korea to return to negotiations on its missile program, Aug. 5, 2017.

Until Trump’s latest remarks, Washington had sent mixed signals to the world this week in its effort to thwart North Korea’s nuclear weapons development in the aftermath of a new round of sanctions unanimously approved last weekend by the United Nations Security Council.

Trump had vowed to attack North Korea, if it continues to threaten the U.S., with a “fire and fury like the world has never seen,” and Mattis said Pyongyang risks annihilation with military action. But Secretary of State Rex Tillerson said “Americans should sleep well at night and have no concerns about this particular rhetoric of the last few days.”

World stock markets, averse to the uncertainty of the standoff, slid for the second day in a row Thursday, with stock indexes in Asia, Europe and the United States all falling a fraction of a percentage point or, at some exchanges, more than 1 percent.

General Kim said that “sound dialogue” is not possible with Trump, calling him a man “bereft of reason” and that “only absolute force can work on him.” He described Trump’s “fire and fury” threat as “a load of nonsense.”

Mattis said Thursday that Trump was “just showing the concern he has, that is shared, obviously, globally.”

If North Korea carries out the missile launch aimed toward Guam, the U.S. could attempt to shoot down the missiles. It has six Aegis ballistic missile defense ships in the region capable of targeting North Korean missiles. But if Pyongyang were to launch the four missiles simultaneously, it could make it harder to shoot down all of them.

Firing the missiles over Japan would ratchet up North Korea’s military adventurism. Its test missiles in recent months, launched at a very high angle, have landed in waters off Japan, although within its economic zone.

A man watches a TV screen showing a local news pro
A man watches a TV screen showing a local news program reporting on North Korea's threats to strike Guam with ballistic missiles, at the Seoul Train Station in Seoul, South Korea, Aug. 10, 2017.

'Stern and strong response'

If the North carries out its missile launch plan aimed near Guam, South Korea said it would draw a “stern and strong” response from Washington and Seoul.

Japan Defense Minister Itsunori Onodera told parliament that a North Korean missile attack on Guam would constitute a Japanese national emergency, saying it would imperil Japan’s existence as a nation.

The threats and counterthreats between Pyongyang and Washington have occurred this week in the days after the U.N. Security Council imposed new, more stringent sanctions on North Korea. The new penalties are intended to reduce Pyongyang’s income from exported goods and labor by at least $1 billion -- one-third of its current annual earnings -- in an effort to end its nuclear weapons development.

The U.S. Defense Intelligence Agency concluded in the past month that North Korea has now miniaturized a nuclear warhead capable of being attached to an intercontinental missile. If Pyongyang does have such capability, it would make North Korea the world’s ninth full-fledged nuclear power. 

Mattis, in a statement Wednesday, said North Korea “should cease any consideration of actions that would lead to the end of its regime and the destruction of its people.” He said North Korea “must choose to stop isolating itself and stand down its pursuit of nuclear weapons.”

He warned that the United States and its allies “now possess the most precise, rehearsed and robust defensive and offensive capabilities on earth,” and that any North Korean military operation “will continue to be grossly overmatched by ours.”

Mattis’ vow came hours after Trump declared in a Twitter comment that the U.S. nuclear arsenal “is now far stronger and more powerful than ever before.”