Washington's goal “is not war” as it seeks to ease high military tension with Pyongyang, US Secretary of Defence Jim Mattis said on Friday, standing at the heavily-fortified border between the two Koreas.

Tension has flared on the Korean peninsula as US President Donald Trump and the North's ruler Kim Jong-Un have traded threats of war and personal insults that sparked global alarm.

But Mattis, who visited the tense Demilitarised Zone during a trip to South Korea, said the US was committed to a “diplomatic solution”.

“As the US Secretary of State Tillerson made clear, our goal is not war but rather the complete, verifiable and irreversible denuclearisation of the Korean peninsula,” he said in the truce village of Panmunjom.

Mattis also stressed he and his South Korean counterpart Song Young-Moo had “made clear our mutual commitment to a diplomatic solution to address North Korea's reckless, outlaw behaviour”.

The remark came a day after Mattis had said Washington was “not rushing to war” and was looking for a “peaceful resolution”.

He is set to hold annual defence talks with Song on Saturday during the two-day trip, which comes ahead of a planned trip by Trump to the South — a key US ally in Asia — next month.

Trump is set to visit Seoul from November 7 to 8 with all eyes on his message to the North and Kim.

The isolated North carried out its sixth nuclear test last month and has launched several missiles in recent months potentially capable of reaching the mainland of its “imperialist enemy” the US.

The moves, staged in violation of UN resolutions banning the North from any use of atomic and ballistic technology, prompted new US-led UN sanctions against the impoverished state.

Pyongyang reacted angrily to new sanctions, and Trump's recent remark that “only one thing will work” with the North fuelled concerns of a potential conflict.

But even some Trump advisers say US military options are limited when Pyongyang could launch an artillery barrage on the South Korean capital Seoul — only around 50 kilometres from the border and home to 10 million people.

The North says its atomic weapons are “treasured sword” to protect itself from potential invasion by the US.