The report has reinforced doubts over whether Trump should push for a second summit with North Korean leader Kim Jong-un when the reclusive sate appears to be pressing ahead with the development of delivery vehicles for its nuclear arsenal.

The US State Department did not comment on whether activity in the reported missile sites would constitute a breach of Kim's agreement with Trump on denuclearization.

But its spokesperson said that a "much brighter future lies ahead" for the North and its people should Kim keep his commitments, including "complete denuclearization and the elimination of ballistic missiles."

Beyond Parallel has located 13 of what it calls an estimated 20 "undeclared" North Korean missile bases. It focused particularly on Sakkanmol, an operational missile base for short-range ballistic missiles that is located 85 kilometers north of the Demilitarized Zone and 135 km northwest of Seoul.

In a commentary posted on 38 North, a website monitoring the North, Leon V. Sigal, the director of the Northeast Asia Cooperative Security Project at the Social Science Research Council, called The New York Times report "misleading."

"Substituting tendentious hyperbole for sound reporting may convince editors to feature a story on page one, but it is a disservice to readers," Sigal wrote.

"There is more than enough to do in negotiating constraints on and the elimination of North Korea's nuclear and missile threats without exaggerating them and prematurely accusing Pyongyang of bad faith or calling into question President Trump's wisdom for trying nuclear diplomacy in earnest," the scholar added. (Yonhap)