Top military officials have warned that North Korea is now able to attach nuclear warheads to missiles.
It’s long been disputed how far the rockets can travel, with tests suggesting a range of a few thousand kilometres.
But a South Korean government briefing, attended by Daily Star Online, revealed that the distance is likely to be far greater.
Lee Sang-hwa, director general of the South's North Korean nuclear affairs bureau, briefed reporters in Seoul last month.
He cited the opinion of US general Joseph Dumford that the missiles posed a direct threat to the US homeland.
His presentation therefore argued that “Europe is also within range” and the whole NATO alliance with it.
Mr Lee did not elaborate on his claim, and neither he nor the foreign ministry have responded to emails for clarification.
A senior ministry source told Daily Star Online that the true extent of North Korea's weapons development was "classified" information.
They said: "I am not able to share everything I know because much of the intelligence is classified and I don't want to go into precise details.
"There are different assessments of North Korea's ballistic missile capabilities, but what is for sure is as they repeat tests, they learn something important."
Chris Ogden, an expert in Asian security at St Andrews University, said the threat to Europe may be exaggerated for "some kind of diplomatic gain".
"But If the information stated is accurate," he said, "it appears to broaden the potential of a nuclear attack emanating from North Korea."
The Hwasong-10 has the longest range of North Korea's current ballistic missiles, spanning 4,000km — far enough to reach central Russia.
While the KN-08, which is still under development, could have an eventual range of 12,000km, bringing all of Europe in range.