North Korea's blast was similar to previous nuclear tests, the Vienna-based monitoring agency CTBTO said early Tuesday, slamming it as a potential threat to international security.
If confirmed as a nuclear test, it would represent "a clear threat to international peace and security...," the agency added in a statement.
"The event shows explosion-like characteristics and its location is roughly congruent with the 2006 and 2009 DPRK (Democratic People's Republic of Korea) nuclear tests," the agency said.
"For now, further data and analysis are necessary to establish what kind of event this is," it added.
"If confirmed as a nuclear test, this act would constitute a clear threat to international peace and security, and challenges efforts made to strengthen global nuclear disarmament and non-proliferation, in particular by ending nuclear testing."
The Comprehensive Test Ban Treaty Organisation is a key authority for providing data on detected nuclear events, but does not identify whether seismic events it picks up are a nuclear explosion, earthquake or chemical blast.