US President Barack Obama's policy of patience with North Korea over its nuclear weapons is failing to pay off as it moves forward with its programme and grows emboldened, the International Institute for Strategic Studies (IISS) said on Thursday.
The IISS warned that Obama's insistence on waiting for Pyongyang to kickstart efforts to re-engage with the international community had so far yielded little.
"So far, strategic patience has not succeeded in bringing about change in North Korea," the London-based group concluded in its annual review of world affairs.
"Pyongyang is instead moving further away from the denuclearisation pledge and closer to projecting nuclear power over long ranges," it said.
The IISS review coincided with reports -- based on new satellite pictures -- that North Korea had restarted operations at the Yongbyon plutonium reactor that it shut down in 2007.
Russia said on Thursday that it too believed North Korea was conducting work at the Yongbyon complex, and warned that the ageing facility was in such a "nightmarish state" it could cause a disaster.
"It is obvious that some works are being conducted, and for a long time at that. According to some signs, steps were indeed being taken to relaunch it," the Interfax news agency quoted a diplomatic source as saying.
The source said that Russia did not have definite information that Pyongyang had restarted the plutonium reactor at Yongbyon, as US analysts have suggested based on the satellite imagery, but warned of dire consequences if this happened.
"Our main concern is linked to a very likely man-made disaster as a consequence. The reactor is in a nightmarish state, it is a design dating back to the 1950s," the source said.
"For the Korean peninsula this could entail terrible consequences, if not a man-made catastrophe."