FORT BRAGG, N.C. — “Storm clouds are gathering” over the Korean Peninsula, Defense Secretary Jim Mattis declared Friday. And as diplomats try to resolve the nuclear standoff, he told soldiers that the U.S. military must do its part by being ready for war.

Without forecasting a conflict, Mattis emphasized that diplomacy stands the best chance of preventing a war if America’s words are backed up by strong and prepared armed forces.

“My fine young soldiers, the only way our diplomats can speak with authority and be believed is if you’re ready to go,” Mattis told several dozen soldiers and airmen at the 82nd Airborne Division’s Hall of Heroes, his last stop on a two-day pre-holiday tour of bases to greet troops.

Mattis’ comments came as the U.N. Security Council unanimously approved tough new sanctions against North Korea, compelling nations to sharply reduce their sales of oil to the reclusive country and send home all North Korean expatriate workers within two years. Such workers are seen as a key source of revenue for North Korean leader Kim Jong Un’s cash-strapped government.

President Donald Trump and other top U.S. officials have made repeated threats about U.S. military action. Some officials have described the messaging as twofold in purpose: to pressure North Korea to enter into negotiations on getting rid of its nuclear arsenal, and to motivate key regional powers China and Russia to put more pressure on Pyongyang so a war is averted.

People watch as a screen shows footage of the launch of a Hwasong-12 rocket, beside a billboard advertising North Korea's Pyeonghwa Motors (R), in Pyongyang on September 16, 2017. North Korea said on September 16 it was seeking military "equilibrium" with the United States as leader Kim Jong-Un vowed to complete Pyongyang's nuclear programme. /KIM WON-JIN/AFP/Getty Images

Kcna Via Kns /, AFP/Getty Images This undated picture released from North Korea's official Korean Central News Agency (KCNA) on Sept. 16, 2017 shows North Korean leader Kim Jong-Un inspecting a launching drill of the medium-and-long range strategic ballistic rocket Hwasong-12 at an undisclosed location. Kim vowed to complete North Korea's nuclear force despite sanctions, saying the final goal of his country's weapons development is "equilibrium of real force" with the United States, state media reported on September 16.

Ahn Young-joon, The Associated Press A woman watches a TV screen showing a file footage of North Korea's missile launch, at the Seoul Railway Station in Seoul, South Korea, Friday, Sept. 15, 2017.



In this photo provided by South Korea Defense Ministry, a Taurus missile fired from a South Korean air force F-15K fighter jet hits a target during a drill, off the country's western coast, South Korea, Wednesday, Sept. 13, 2017. South Korea says it conducted its first live-fire drill for an advanced air-launched cruise missile it says will strengthen its pre-emptive strike capability against North Korea in the event of crisis. (South Korea Defense Ministry via AP).

Eugene Hoshiko, The Associated Press A man watches a TV news program on a public screen showing an image of North Korean leader Kim Jong Un while reporting North Korea's possible nuclear test in Tokyo Sunday, Sept. 3, 2017. South Korea's military said Sunday that North Korea is believed to have conducted its sixth nuclear test after it detected a strong earthquake, hours after Pyongyang claimed that its leader has inspected a hydrogen bomb meant for a new intercontinental ballistic missile.

Shizuo Kambayashi, Associated Press file In this Aug. 6, 2017, file photo, a man takes a photo of a TV news program in Tokyo, showing an image of North Korean leader Kim Jong Un. U.N. experts say North Korea illegally exported coal, iron and other commodities worth at least $270 million to China and other countries including India, Malaysia and Sri Lanka during the six-month period ending in Aug. in violation of U.N. sanctions.



KRT via AP Video, Associated Press file In this Dec. 12, 2012 file image made from video, North Korea's Unha-3 rocket lifts off from the Sohae launching station in Tongchang-ri, North Korea. North Korea's top governing body warned Thursday, Jan. 24, 2013 that the regime will conduct its third nuclear test in defiance of U.N. punishment, and made clear that its long-range rockets are designed to carry not only satellites but also warheads aimed at striking the United States.

Greg Baker, AFP/Getty Images The North Korean town of Sinuiju (at rear) is seen behind the Friendship Bridge (L) which connects Sinuiju and the the Chinese border city of Dandong, and the Broken Bridge (R), in Dandong, in China's northeast Liaoning province on Sept. 4, 2017. Countries around the world swiftly condemned North Korea's announcement that it had tested a hydrogen bomb on September 3, with South Korea calling for the "strongest punishment" against Pyongyang while key ally China strongly condemned it. The Broken Bridge was bombed during the Korean War and now reaches only half way across the river.

Greg Baker, AFP/Getty Images Lights are seen in the North Korean town of Sinuiju, behind the Friendship Bridge (L) which connects Sinuiju and the the Chinese border city of Dandong, and the Broken Bridge (R), in Dandong, in China's northeast Liaoning province on Sept. 3, 2017. Countries around the world swiftly condemned North Korea's announcement that it had tested a hydrogen bomb on September 3, with South Korea calling for the "strongest punishment" against Pyongyang while key ally China strongly condemned it. The Broken Bridge was bombed during the Korean War and now reaches only half way across the river.



Yonhap, AFP/Getty Images South Korea's Capital Defense Command soldiers take part in a military drill in Seoul on Sept. 4, 2017. Following North Korea's sixth nuclear test, South Korean President Moon Jae-In called for the "strongest punishment" while top military officers in Seoul and Washington vowed a joint "military counteraction" at the earliest date.

Ahn Young-joon, The Associated Press South Korean army's K-1 tanks move during a military exercise in Paju, South Korea, near the border with North Korea, Monday, Sept. 4, 2017. Following U.S. warnings to North Korea of a "massive military response," South Korea's military on Monday fired missiles into the sea to simulate an attack on the North's main nuclear test site a day after Pyongyang detonated its largest ever nuclear test explosion.

Greg Baker, AFP/Getty Images A North Korean soldier stands on the bank of the Yalu river near the North Korean town of Sinuiju, opposite the Chinese border city of Dandong, in China's northeast Liaoning province on Sept. 4, 2017. The five-nation BRICS grouping meeting in China said on September 4 it "strongly deplores" North Korea's latest nuclear test, adding to global condemnation of Pyongyang.



Ahn Young-joon, The Associated Press South Korean army soldiers take positions with their K-55 self-propelled howitzers during a military exercise in Paju, South Korea, near the border with North Korea, Monday, Sept. 4, 2017. North Korea said it set off a hydrogen bomb Sunday in its sixth nuclear test, which judging by the earthquake it set off appeared to be its most powerful explosion yet.

Korean Central News Agency/Korea News Service via AP In this undated image distributed on Sunday, Sept. 3, 2017, by the North Korean government, shows North Korean leader Kim Jong Un at an undisclosed location. North Korea’s state media on Sunday, Sept 3, 2017, said leader Kim Jong Un inspected the loading of a hydrogen bomb into a new intercontinental ballistic missile, a claim to technological mastery that some outside experts will doubt but that will raise already high worries on the Korean Peninsula. Independent journalists were not given access to cover the event depicted in this image distributed by the North Korean government. The content of this image is as provided and cannot be independently verified.

Eugene Hoshiko, Associated Press file In this Aug. 29, 2017 file photo, Japanese Air Self-Defense Force (JASDF) demonstrates the training to utilize the PAC-3 surface to air interceptors at the U.S. Yokota Air Base in Fussa, on the outskirts of Tokyo. Japan is debating whether to develop limited pre-emptive strike capability and buy cruise missiles - ideas that were anathema in the pacifist country before the North Korea missile threat. Japan currently has a two-step missile defense system, interceptors on destroyers in the Sea of Japan, and if they fail, surface-to-air PAC-3s.



Yonhap News/Newscom/Zuma Press/TNS North Korean leader Kim Jong-un presides over a military parade held in Pyongyang to mark the 105th birthday of late founder Kim Il-sung on April 15, 2017.

Wong Maye-E, Associated Press file In this April 15, 2017, file photo, North Korean leader Kim Jong Un waves during a military parade in Pyongyang, North Korea.

KRT via AP Video This image made from video aired by North Korea's KRT on Aug. 26, 2017 shows a photo of North Korean leader Kim Jong Un inspecting soldiers during what Korean Central News Agency called a "target=striking contest" at unknown location in North Korea.



Kim Kwang Hyon, The Associated Press North Koreans watch a televised news broadcast of the test-fire of a ballistic rocket Wednesday in Pyongyang, North Korea. On Tuesday, North Korea fired an intermediate-range missile directly over Japan -- the type of missile that could reach American, South Korean and Japanese military bases in northeast Asia.

Lee Jin-man, Associated Press file In this Tuesday, April 23, 2013, file photo, a North Korean soldier looks at the southern side through a pair of binoculars at the border village of Panmunjom, which has separated the two Koreas since the Korean War, in Paju, north of Seoul, South Korea. Threatening to fire a volley of missiles toward a major U.S. military hub _ and the home to 160,000 American civilians _ may seem like a pretty bad move for a country that is seriously outgunned and has an awful lot to lose. But pushing the envelope, or just threatening to do so, is what North Korea does best.

Ahn Young-joon, The Associated Press South Korean army soldiers patrol along the barbed-wire fence in South Korea's Paju near the border with North Korea, Friday, Aug. 11, 2017.



Yosuke Mizuno. Kyodo News via AP A PAC-3 interceptor unit arrives at a garrison of the Japan Ground Self-Defense Force in Kaita, Hiroshima prefecture, southwestern Japan, Saturday, Aug. 12, 2017. Japan started deploying land-based Patriot interceptors after North Korea threatened to send ballistic missiles flying over western Japan and landing near Guam. The Defense Ministry said Friday the PAC-3 surface-to-air interceptors are being deployed at four locations - Hiroshima, Kochi, Shimane and Ehime.

For the military, the focus has been on ensuring soldiers are ready should the call come.

At Fort Bragg, Mattis recommended the troops read T.R. Fehrenbach’s military classic “This Kind of War: A Study in Unpreparedness,” first published in 1963, a decade after the Korean War ended.

“Knowing what went wrong the last time around is as important as knowing your own testing, so that you’re forewarned – you know what I’m driving at here,” he said as soldiers listened in silence. “So you gotta be ready.”

The U.S. has nearly 28,000 troops permanently stationed in South Korea, but if war came, many thousands more would be needed for a wide range of missions, including ground combat.

The retired Marine Corps general fielded questions on many topics in his meetings with troops at Guantanamo Bay naval base in Cuba and Naval Station Mayport in Florida on Thursday and at Camp Lejeune and Fort Bragg in North Carolina on Friday. North Korea seemed uppermost on troops’ minds as they and their families wonder whether war looms.

Asked about recent reports that families of U.S. service members in South Korea might be evacuated, Mattis stressed his belief that diplomacy could still avert a crisis. He said there is no plan now for an evacuation.

“I don’t think it’s at that point yet,” he said, adding that an evacuation of American civilians would hurt the South Korean economy. He said there is a contingency plan that would get U.S. service members’ families out “on very short notice.”

Mattis said he sees little chance of Kim disrupting the Winter Olympics, which begin in South Korea in February.

“I don’t think Kim is stupid enough to take on the whole world by killing their athletes,” he said.

Mattis repeatedly stressed that there is still time to work out a peaceful solution. At one point he said diplomacy is “going positively.” But he also seemed determined to steel U.S. troops against what could be a costly war on the Korean Peninsula.

“There is very little reason for optimism,” he said.