SEOUL, South Korea – North Korea apparently conducted a widely anticipated nuclear test Tuesday, strongly indicated by an "explosion-like" earthquake that monitoring agencies around the globe said appeared to be unnatural.

There was no confirmation from Pyongyang that it had conducted a test, which it has been threatening for weeks.

Any test would be seen as another big step toward North Korea's goal of building a warhead that can be mounted on a missile. It would also be a bold signal from young leader Kim Jong Un, who took power in December 2011 following the death of his father, Kim Jong Il.