Seoul: North Korean state media warned the United States of a "super-mighty preemptive strike" after US Secretary of State Rex Tillerson said the United States was looking at ways to bring pressure to bear on North Korea over its nuclear program.

US President Donald Trump has taken a hard line with North Korean leader Kim Jong-un, who has rebuffed admonitions from sole major ally China and proceeded with nuclear and missile programmes in defiance of UN Security Council sanctions.

The Rodong Sinmun, the official newspaper of the North's ruling Workers' Party, did not mince its words.

"In the case of our super-mighty preemptive strike being launched, it will completely and immediately wipe out not only US imperialists' invasion forces in South Korea and its surrounding areas but the US mainland and reduce them to ashes," it said.