SEOUL: US Secretary of Defense Jim Mattis on Saturday warned North Korea of a "massive military response" to any use of nuclear weapons as tensions remain sky-high ahead of Donald Trump’s visit to South Korea.

Pyongyang in recent months has sparked global alarm by conducting a sixth nuclear test and test-launching missiles capable of reaching the US mainland, while Trump and the North’s young ruler Kim Jong-Un have traded threats of war and personal insults.
Mattis, on a trip to Seoul for annual defence talks, maintained that diplomacy remained a "preferred course of action" but stressed, "our diplomats are most effective when backed by credible military force".

"Make no mistake -- any attack on the United States or our allies will be defeated," Mattis said at a joint press conference with his South Korean counterpart Song Young-Moo.

"Any use of nuclear weapons by the North will be met with a massive military response, effective and overwhelming," Mattis said, adding Washington "does not accept a nuclear North Korea."

Mattis did not specify the type of nuclear weapon use that would prompt a military response. Pyongyang’s Foreign Minister Ri Yong-Ho said on the sidelines of the UN General Assembly last month that his country could test a nuclear bomb over the Pacific.

Mattis also urged Pyongyang to "harbour no illusion", saying the isolated state is militarily "overmatched" by the US and South Korea -- a key ally of Washington that hosts 28,500 US troops.