Defense Secretary Jim Mattis warned North Korean dictator Kim Jong-un on Wednesday that his regime and his people would be destroyed in a conflict with the U.S.

In a statement, Mattis said Kim should "take heed" of the "fire and fury" warnings from President Donald Trump and cease his threats and provocations.

"The United States and our allies have the demonstrated capabilities and unquestionable commitment to defend ourselves from an attack," Mattis said, despite Kim's boast of having nuclear weapons and the ability to deliver them against the U.S. mainland with Intercontinental Ballistic Missiles (ICBMs).

"Kim Jong-un should take heed of the United Nations Security Council's unified voice, and statements from governments the world over, who agree the DPRK (Democratic People's Republic of Korea) poses a threat to global security and stability," Mattis said.

"The DPRK must choose to stop isolating itself and stand down its pursuit of nuclear weapons," Mattis said. "The DPRK should cease any consideration of actions that would lead to the end of its regime and the destruction of its people."

In another show of U.S. strength, two B-1B Lancer bombers operating out of Guam flew over South Korea on Tuesday ahead of major joint ground, sea and air exercises later this month to demonstrate readiness against North Korean threats.

The flyover came on the same day that Jong-un threatened a missile attack on Guam following Trump's "fire and fury" warning to North Korea.

U.S. Air Forces Pacific said in a statement that the B-1Bs from 37th Expeditionary Bomb Squadron at Ellsworth Air Force Base, South Dakota, flew from Andersen Air Force Base, Guam, on a 10-hour mission.

The bombers were accompanied by two Japan Air Self Defense Force F-2 fighter jets and by two Republic of Korea Air Force KF-16 fighters.

"As demonstrated today, our air forces stand combat-ready to deliver airpower when called upon," said Lt. Col. Daniel Diehl, commander of the 37th EBS.

"How we train is how we fight and the more we interface with our allies, the better prepared we are to fight tonight," one of the B-1B pilots was quoted as saying by Air Forces Pacific. B-1Bs out of Guam last flew over South Korea on July 30.

Also on Tuesday, the Korean Central News Agency, North Korea's propaganda outlet, said the North is "examining the operational plan" to strike the U.S. territory of Guam with medium- and long-range ballistic missiles. KCNA said that a strike on Andersen AFB would "send a serious warning signal to the U.S."

The KCNA statement came hours after Trump at his estate in Bedminster, N.J., said that North Korea would "face fire and fury like the world has never seen" unless it stopped threatening the U.S. and its allies.

Guam's governor, Eddie Baza Calvo, released a video address Wednesday, stating that there has been no change to the threat level on the island despite the pointed warnings from North Korea.

"I want to reassure the people of Guam that currently there is no threat to our island or the Marianas," he said. "I also want to remind national media that Guam is American soil and we have 200,000 Americans in Guam and the Marianas. We are not just a military installation."

Since 2015, Guam has been defended by the U.S. Army's Terminal High Altitude Area Defense (THAAD) anti-missile system.

The U.S. currently has two THAAD launchers in place on a former golf course south of Seoul and has repeatedly pressed South Korea to deploy the full battery.

North Korea has repeatedly denounced the THAAD deployment and escalated its threats after the United Nations Security Council voted 15-0 last week to impose tougher sanctions on the North. China, North Korea's chief trading partner, voted in favor of the sanctions.

The sanctions vote came after North Korea in July conducted two successful test launches of an Intercontinental Ballistic Missile (ICBM), called the Hwasong 14, with the range to hit the U.S. mainland.

The Washington Post reported Tuesday that the U.S. Defense Intelligence Agency has concluded that North Korea has also successfully miniaturized a nuclear warhead to fit atop the Hwasong 14.

Despite the ominous developments, South Korean officials said the situation on the peninsula has not yet reached the crisis stage.

An official at South Korea's presidential office said the increasingly bellicose statements from the North are an overreaction to the U.N. sanctions. "Pyongyang seems to be overly sensitive to the U.N. sanctions. Its threat on Guam appears to be aimed at boosting internal solidarity," the official said, according to South Korea's Yonhap news agency.

The official said the threats would only increase as the U.S., South Korea and several allies prepare for joint military exercises on the peninsula beginning Aug. 21.

"The situation is bad now, and it's going to get worse in August; it's going to get much more dangerous in August," Joel Wit, a senior fellow at US-Korea Institute and former State Department official, said in a Aug. 2 conference call with reporters organized by 38 North, a website for analysis of Korean defense issues.

While denouncing the annual Ulichi Freedom-Guardian exercises, North Korea has also dangled the possibility of suspending its nuclear programs if the joint training by more than 25,000 U.S. and South Korean troops were canceled. The North has repeatedly called the Ulichi exercises a dress rehearsal for invasion.

Air Forces Pacific last week announced that 12 F-16s and 200 Wisconsin Air National Guardsmen would join in the Ulichi exercises later this month.

The jets from the 176th Fighter Squadron will fly out of Kunsan Air Base during a four-month rotation, Air Forces Pacific said, and they will train under the direction of the 8th Fighter Wing.

In a surprise stop in Guam pn Wednesday on his way home from the region, Secretary of State Rex Tillerson defended Trump's "fire and fury" remarks while stating that the U.S. is not under "imminent threat" of a nuclear attack from North Korea.

"Americans should sleep well at night," Tillerson said as he flew from Malaysia to Washington, stopping in Guam to refuel.

South Korean President Moon Jae-in also called for calm following an hour-long phone call with Trump on Monday night.

"Above all, President Moon emphasized that South Korea can never accept a war erupting again on the Korean Peninsula," his office said in a statement after the phone call. "He stressed that the North Korean nuclear issue must be resolved in a peaceful, diplomatic manner through a close coordination between South Korea and the United States."

-- Richard Sisk can be reached at Richard.Sisk@Military.com.