North Korea last week tried out a new engine for a developmental strategic ballistic missile, unidentified government insiders told the Yonhap News Agency on Sunday.
"It appears that North Korea conducted the engine test aimed at extending the range of the KN-08 missile to over [3,100 miles]," an insider said.
"If the North decides the test [was] successful, it is expected to operationally deploy the new long-range rocket," he continued.
The trial reportedly occurred the day prior to the North's Jan. 12 nuclear test.
The alleged test took place at the North's Dongchang-ri missile launch complex. Recent satellite photographs of the isolated country's Musudan-ri site indicate the pace of work on a new launchpad has increased ahead of a feared launch of another long-range rocket.
The South Korean Defense Ministry announced on Monday it is closely monitoring the North's missile sites and its atomic testing grounds at Punggye-ri for indications that new launches or nuclear detonations are in the works, Yonhap separately reported.