US Defence Secretary Ashton Carter on Sunday visited the Demilitarised Zone (DMZ) dividing the Korean peninsula and renewed calls for North Korea to avoid provocations and step away from its nuclear programme.

On a brief trip to the heavily mined area that for 60 years has been a buffer between the Koreas, Carter and South Korean Defence Minister Han Min-Koo stood atop a hill known as Observation Post Ouellette -- the closest post to the demarcation line between the two nations.

Carter later said the United States remains committed to the six-party talks process that seeks the denuclearisation of the peninsula.

"That remains our policy," he told reporters. "We remain committed to achieving that negotiated outcome with North Korea, and believe that they should be on the path of doing less -- and ultimately zero -- in the nuclear field, not to be doing more."

North Korea has carried out three nuclear tests and has explicitly indicated its intention to carry out a fourth.

It abandoned the six-party talks, which also grouped South Korea, China, Russia, the US and Japan, in April 2009.

"We continue to call on North Korea to maintain peace and stability on the peninsula, avoid provocations, avoid adding to tensions on the peninsula and to take the steps that are called for in the six-party talks to denuclearise the peninsula," the Pentagon chief said.

Carter, wearing a casual black jacket and hiking shoes, spent about 10 minutes peering at the fence and wooded area that leads into North Korea.

He then went to the nearby Joint Security Area, where soldiers from either side of the border stand facing each other only yards apart.

At one point, a pair of North Korean soldiers marched to within a short distance of their side of the border and made a show of photographing visitors across the way.

"Being here shows you up close just how dangerous this part of the world is," Carter said. "That's why our alliance with South Korea is iron-clad and strong."

About 28,500 US troops are stationed in South Korea and the two forces have very close military ties.

- Ready to 'fight tonight' -

In the 62 years since an armistice was signed in the 1950-53 Korean War, numerous incidents and clashes -- most instigated by North Korea -- have threatened the official ceasefire.

Because the truce was never ratified by a formal peace treaty, the two Koreas technically remain at war, and Pyongyang has in the past put its troops on a war footing during times of high tension.

"The ever-present danger is the reason why we speak of the ability to 'fight tonight' -- that's the slogan up here," Carter said.

"No one ever wants to have to do that, but deterrence is guaranteed through strength and that's what the alliance (with South Korea) is all about."

In August this year North Korean leader Kim Jong-Un put his frontline troops on alert following a rare artillery exchange across the border.

That crisis was rooted in landmine blasts that maimed two South Korean soldiers on patrol along the border.

Seoul blamed Pyongyang and responded by switching on banks of giant speakers, which had lain silent for more than a decade, and blasting propaganda messages into North Korea

The North denied any involvement and threatened to attack the propaganda units as cross-border military tensions soared. The two sides eventually stepped back from conflict after marathon talks.

Carter's visit to the DMZ was his first international stop on an eight-day trip mainly focused on the Asia-Pacific.

He will meet leaders from more than a dozen nations across East and South Asia. Officially, his mission is intended to help push the next phase of America's foreign policy "rebalance" to the strategically important region.

But a central theme is likely to be China's construction of artificial islands in the South China Sea and its claims of sovereignty over almost the entire waterway.

He visited Alaska on his way around the globe, stopping near the Arctic Circle to reiterate to US troops in Fairbanks the region's strategic importance.

Later Sunday Carter was to attend a US-South Korea security meeting in Seoul. He leaves Monday for an Association of Southeast Asian Nations defence ministers' meeting in Kuala Lumpur.