The DPRK is near to restart its nuclear reactor, State Department spokesman Sean McCormack told reporters.

They are moving "closer and closer to that point where they are to the point of operationalizing Yongbyon again. They haven't got that point yet and we would urge them not to get to that point," McCormack said.

The spokesman warned that Pyongyang must halt its nuclear activities or it will be isolated.

The DPRK announced earlier in the day that it has begun the work to restore its nuclear facilities in Yongbyon "to their original state."

It was a "counter-measure" against the United States for not sticking to its promise of delisting the DPRK from a "state sponsor of terrorism" blacklist, DPRK Foreign Ministry spokesman said.

The DPRK blew up on June 27 the cooling tower of its atomic reactor to demonstrate its commitment to nuclear disarmament, a day after handing over details of its atomic programs.

Under the 2007 pact, the DPRK pledged to disable its nuclear program in a step toward its eventual dismantlement in exchange for diplomatic concessions and energy aid. But the accord has been stalled due to disputes over the verification of a nuclear declaration between the DPRK and United States.