Pyongyang's state media said last week's test successfully verified the atmospheric re-entry of the warhead loaded on the test-launched missile, which experts say may be able to reach the U.S. state of Alaska.
However, Yi Wan-young, who is also a member of South Korean parliament's intelligence committee, told reporters during a televised briefing that South Korea's National Intelligence Service has not been able to confirm that re-entry was successful.
"Considering how North Korea does not have any testing facilities (for re-entry technology), the agency believes (North Korea) has not yet secured that technology," he said.
Yi said the agency believed the missile launched last week was a modified version of the KN-17 intermediate range missile that was tested in May.
He also said the agency had not detected any unusual activity at North Korea's Punggye-ri nuclear test site.