North Korea will pursue its "defensive" nuclear programme as long as it feels threatened by the United States, its UN disarmament envoy in Geneva said on 13 August.

In a rare interview, Ambassador So Se Pyong also denounced the latest joint US-South Korean military exercises, due to start next week, saying they fanned tensions on the divided peninsula as it marks the 70th anniversary of liberation from Japanese occupation at the end of World War Two.

"They have to change their attitude, their hostile policies attitude and otherwise, as we mentioned strictly as the country's policy, we'll continue the simultaneous development of the economy and the nuclear program," he told Reuters.

So Se Pyong said the program was defensive but warned that if war broke out with rivals his country would be prepared.

"When at the second Korean war, then, no problem. Now DPRK is different from 1950's. We can make any kind of things against that," said So, who is the Democratic Republic of Korea's ambassador to the United Nations in Geneva and to its Conference on Disarmament.

So denied that North Korea had played any role in laying land mines that exploded in the Demilitarised Zone border last week, injuring two South Korean soldiers. South Korea's military has threatened retaliation after it accused Pyongyang of planting the mines, calling it an act of provocation.

"If something happens in South Korea, they blame the North - (for) everything. A few years before there was the incident of the ship which was sank, they blamed the North also," So said.

"How can we make that small notorious things if there is a kind of big military actions, then we have to make the account, you know the actions. A small thing, for what purpose," he added.

When asked about reports that North Korea might be preparing another underground nuclear test or long-range missile launch, he said that is was top secret.

South Korea said on Thursday its president, Park Geun-hye, would hold an Oct. 16 summit in Washington with US President Barack Obama to discuss issues including North Korea's nuclear programme.