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 programs in defiance of United Nation- imposed sanctions.
The Rodong Sinmun, the official newspaper of the North's ruling Workers Party, did not mince its words, saying: "In the case of our super-mighty preemptive strike being launched, it will completely and immediately wipe out not only US imperialist invasion forces in South Korea and its surrounding areas but in the US mainland and reduce them to ashes."
North Korea threatens regularly to destroy Japan, South Korea and the United States and has shown no let-up in its belligerence after a failed missile test on Sunday, a day after putting on a huge display of missiles at a parade in Pyongyang.
Besides Tillerson saying on Wednesday that Washington is seeking new ways to pressure Pyongyang "to re-engage with us," US Vice President Mike Pence, on a tour of Asian allies, has said repeatedly an "era of strategic patience" with North Korea is over.
Meanwhile, South Korean and US air forces continued with an annual training exercise, which is due to run to April 28. But there were questions about where an aircraft carrier-led US naval task force was bound in North Asia.