By Mick Krever, CNN

(CNN) -- South Korea believes there is "no concrete evidence" that North Korea has mastered the technology to deliver a nuclear warhead on an intercontinental ballistic missile, the country's foreign minister has told CNN.

Kang Kyung-wha told CNN's Christiane Amanpour in an exclusive interview taped Monday that while North Korea's weapons program had developed far faster than expected, Pyongyang had yet to demonstrate it had achieved some key technical capabilities that would show it could successfully fire a nuclear warhead.

"They haven't demonstrated their reentry capability," she said. "They haven't demonstrated their remote targeting, or the miniaturization that is required to do this."

Kang admitted that the North Koreans have developed their program at "a pace that's far faster than many of us have expected -- but they have not reached the final completion stage yet."

"North Korea will never be accepted as a nuclear power," she said, adding that only a "peaceful resolution" was acceptable.

Some American experts are increasingly suggesting that the only realistic policy toward North Korea is deterrence, as with the former Soviet Union.

"We're going to have to learn to live with this," Jeffrey Lewis of the Middlebury Institute of International Studies at Monterey told Amanpour last Wednesday. "We now need to start to look at the situation realistically and realize, even if we can't achieve denuclearization, we still have interest in having a stable deterrent relationship with North Korea."

South Korea's defense ministry determined last week that the missile tested last Wednesday was a new type of ICBM.

"It is clearly different from the Hwasong-14 in terms of the appearance of the warhead, the overall size and the connecting part between the first and second stages," Col. Roh Jae-cheon, spokesman for South Korea's Joint Chiefs of Staff, said.

Yeo Suk-joo, policy chief for the defense ministry, told South Korean Parliament on Friday that further review was needed to assess the missile's reentry technology, guidance and warhead operation.

South Korea ignores 'the daily comments'

The standoff with North Korea has been marked by an escalating war of words -- a war that the American president has been all too happy to engage in.

"Why would Kim Jong-un insult me by calling me 'old,' when I would NEVER call him 'short and fat?'" President Trump tweeted in November.

North Korea, for its part, has called Trump an "old lunatic."

"We don't go by the daily comments, we go by the longer-term patterns," Kang told Amanpour.