The ministry did acknowledge that Pyongyang was on a fast-track to developing an intercontinental ballistic missile capable of reaching the US mainland, but as all matters linked with the isolated country are, said it was hard to be more specific as the North has never test-fired one.
"If the missile is threatening it will be intercepted", he said.
Carter, whose two-year run as Pentagon chief will come to an end when President Barack Obama leaves office January 20, said in his final news conference that it might make sense to watch such a test without taking action.
Analysts are divided over how close Pyongyang is to realizing its full nuclear ambitions, especially since it has never successfully test-fired an intercontinental ballistic missile.
The North has a "considerable" ability to produce weapons from highly-enriched uranium, the paper said. Citing a series of launch failures for the already-deployed road-mobile intermediate-range Musudan missile, an official explained that it is hard to determine the stability of the North's longer-range weapons.
U.S. think tank the Institute for Science and International Security estimated in June that the North's total nuclear arsenal stood at more than 21 bombs - up from 10-16 weapons in 2014 - based on estimates of the country's plutonium and uranium stocks.
The North has boosted pluto- nium supplies by reactivating its once-mothballed nuclear reactor in Yongbyon, the South's defence ministry said. The type of plutonium needed for a nuclear bomb is typically extracted from spent nuclear reactor fuel.
In his annual New Year's address, North Korean leader Kim Jong-un said the country is making final preparations to test its first ICBM.
The previous week, Trump made a statement via Twitter that the development was "not going to happen", and vowed to halt Pyongyang in its tracks.
The ministry also said the country developed a hydrogen bomb and "had access to standardized nuclear warheads by bolstering up its nuclear weapons on a high level at an unimaginably high speed on the strength of self-development" despite the worldwide sanctions.