US Vice President Mike Pence on Monday said that his country's "era of strategic patience" with North Korea is over and warned Pyongyang not to test the resolve of the US.
Speaking in Seoul, Pence linked recent US military strikes in Syria and Afghanistan with the situation in North Korea, saying they showed the "strength and resolve of our new President."
Pence arrived in Seoul on Sunday, hours after North Korea carried out a failed missile launch, CNN reported.
"We will defeat any attack and we will meet any use of conventional or nuclear weapons with an overwhelming and effective response," Pence said, adding that when it came to North Korea "all options are on the table".
On Monday, the US and South Korea launched a joint air force military exercise to ensure readiness against North Korea, according to the South Korean media.
Tensions on the peninsula have ratcheted up in recent weeks, amid tit-for-tat sabre-rattling from the US and North Korea and analysts' warnings that North Korea was preparing for a sixth nuclear test, CNN reported.
Amid concerns the US might launch a preemptive strike on North Korea, Pence said Washington would "closely consult" with Seoul "as we make decisions moving forward."
Earlier in the day, Pence visited the Korean demilitarized zone (DMZ), which he described as the "frontier of freedom", according to the report.
The DMZ is the highly-fortified de facto border between North and South Korea.
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.
He reiterated US support for South Korea, telling his host: "We are with you 100%".
Hwang hailed the early deployment of the controversial US missile defence system (known as THAAD) designed to protect against threats from North Korea.
Pence said he was disappointed that China had taken retaliatory actions against South Korea in response to the move.
The US has leaned on China -- North Korea's main ally -- to apply pressure on Pyongyang to curtail its nuclear ambitions.
At the same time, the US has increased its military footprint in the region by deploying a naval carrier strike group to waters off the Korean Peninsula.
Pence said on Monday that Trump was "very hopeful that China will take actions to bring about a change of policy in North Korea. An abandonment of its nuclear weapons programme and its ballistic missile programme."
The US Vice-President will leave for Japan on Tuesday. His trip includes visits to Indonesia and Australia.