US Secretary of Defense James Mattis says that North Korea “shackles its people” in order to threaten the world “with catastrophe”.

Mr Mattis said that the US government is doing “everything we can” to solve the ongoing crisis with North Korea, but noted that the provocations have continued even though Pyongyang has been on the receiving end of unanimous condemnation from the United Nations Security Council.

North Korea is “an oppressive regime that shackles its people, denying their freedom, their welfare, and their human dignity in pursuit of nuclear weapons, and their means of delivering in order to threaten others with catastrophe,” Mr Mattis said, according to NBC News.

Mr Mattis noted during his visit to the Demilitarized Zone — which was described as tense but eerily quiet by the Associated Press — that their attempts at diplomacy are backed up by a strong US military.

“We’re doing everything we can to solve this problem diplomatically — everything we can,” he told troops in South Korea after stepping off the Black Hawk helicopter that had flown him to the DMZ, which is 25 miles north of central Seoul.

“Ultimately, our diplomats have to be backed up by strong soldiers and sailors, airmen and Marines,” he added, “so they speak from a position of strength, of combined strength, of alliance strength, shoulder to shoulder.”

Kim Jong-un inspects weapon North Korea says is powerful hydrogen bomb Show all 6 1 /6 Kim Jong-un inspects weapon North Korea says is powerful hydrogen bomb Kim Jong-un inspects weapon North Korea says is powerful hydrogen bomb Photos released by North Korea show Kim Jong-un talking to subordinates next to a device thought to be the new thermonuclear weapon. There is no way of independently verifying the pictures STR/AFP/Getty Images Kim Jong-un inspects weapon North Korea says is powerful hydrogen bomb North Korea claims it has successfully tested an advanced hydrogen bomb which could be loaded onto an intercontinental ballistic missile AFP/Getty Kim Jong-un inspects weapon North Korea says is powerful hydrogen bomb A diagram on the wall behind Mr Kim shows a bomb mounted inside a cone STR/AFP/Getty Images Kim Jong-un inspects weapon North Korea says is powerful hydrogen bomb North Korean leader Kim Jong-Un (C) attending a photo session with participants of the fourth conference of active secretaries of primary organisations of the youth league of the Korean People's Army (KPA) in Pyongyang STR/AFP/Getty Images Kim Jong-un inspects weapon North Korea says is powerful hydrogen bomb A new stamp issued in commemoration of the successful second test launch of the "Hwasong-14" intercontinental ballistic missile KCNA via Reuters Kim Jong-un inspects weapon North Korea says is powerful hydrogen bomb A new stamp issued in commemoration of the successful second test launch of the "Hwasong-14" intercontinental ballistic missile KCNA via Reuters

Tension between Washington and Pyongyang have heightened since President Donald Trump was sworn into office earlier this year, as North Korea has repeatedly tested missiles that they say could hit the United States mainland. North Korea has also tested their nuclear capacities.

Mr Trump has led the international community to impose strict sanctions on North Korea for those tests and development, even attracting support for the sanctions from China.