US Vice-President Mike Pence has said his country’s “era of strategic patience” with North Korea is over.
Mr Pence first made the remarks at the demilitarised zone (DMZ), the area dividing the two Koreas, during a visit to South Korea to reaffirm ties.
His visit comes amid escalated tensions on the peninsula, with heated rhetoric from both North Korea and the US.
He arrived in Seoul on Sunday hours after North Korea carried out a failed missile launch.
On Monday, the US and South Korea launched a joint air force military exercise to ensure readiness against North Korea, according to South Korean media.
Mr Pence, whose father served in the Korean War, visited the truce village of Panmunjom, where the war’s armistice was signed.
‘Don’t test US resolve’
Speaking alongside South Korea’s acting President Hwang Kyo-ahn later, he said North Korea had conducted nuclear and missile tests as the previous US administration had observed a policy of “strategic patience”, but this was now over. Pence Message
“Just in the past two weeks, the world witnessed the strength and resolve of our new president in actions taken in Syria and Afghanistan,” Mr Pence said.
“North Korea would do well not to test his resolve or the strength of the armed forces of the United States in this region.”
He reiterated US support for South Korea, telling his host: “We are with you 100%.” Pence Message to sount Korea
Mr Hwang hailed the early deployment of the controversial US missile defence system (known as Thaad) designed to protect against threats from North Korea.
The US vice-president said he was disappointed that China had taken retaliatory actions against South Korea in response to the move.
Mr Pence’s latest comments echoed those made by Secretary of State Rex Tillerson, who warned that pre-emptive military action was “on the table” when he visited the DMZ last month.
Russia’s Foreign Minister Sergei Lavrov said Moscow would not tolerate “missile adventures by Pyongyang” but a unilateral use of power by the US would be “a very risky course”.
Mr Pence earlier went to Camp Bonifas, a United Nations military compound near the DMZ.
Mr Pence is visiting South Korea, Japan, Indonesia and Australia on a 10-day Asia tour.
On Sunday, Lt Gen HR McMaster, the US top security adviser, said his country was working on a “range of options” with China, the first confirmation the two countries were co-operating to find a solution to the North Korean issue.
US President Donald Trump also said on Sunday that Beijing was “working with us on the North Korean problem”. He had stated last week that the US and its allies may “deal with” Pyongyang if China did not.
The BBC’s Stephen Evans in Seoul says US policy now seems to be to persuade China to contain North Korea while keeping the economic and military pressure on.
China, historically Pyongyang’s sole major ally, has reiterated its call for North Korea to stop all tests, and has also called for a peaceful solution.
Besides Sunday’s launch, North Korea has held a series of large-scale events in the past week including a massive celebration and military parade on Saturday.
It has denounced the US deployment of an aircraft carrier group to the region, saying it would respond by “force of arms” to “reckless moves”.
Observers have said North Korea may conduct a sixth nuclear test soon, with activity reported at nuclear facilities, according to the website 38 North.
Meanwhile about 1,000 US airmen and fighter jets are taking part in a combat training exercise in South Korea, reported Yonhap news agency. South Korea has sent about 500 personnel and planes. The Max Thunder exercise will last for two weeks.