North Korea's uranium enrichment facility has doubled in size over the last few years, the UN's atomic watchdog chief has warned, as global tensions grow over Pyongyang's burgeoning nuclear weapons programme.
Yukiya Amano, head of the International Atomic Energy Agency (IAEA) told the Wall Street Journal that the isolated state's nuclear capacities are being ramped up.
"The situation is very bad... It has gone into a new phase," Amano said, in the report published Monday. "All of the indications point to the fact that North Korea is making progress, as they declared."
International alarm over Pyongyang's military ambitions has risen after a series of missile launches and nuclear tests last year, and earlier this month it fired four rockets in what it described as practice for an attack on United States military bases in Japan.
The North, which also tested a powerful new rocket engine at the weekend to coincide with a trip to Asia by US Secretary State Rex Tillerson, has long coveted a missile capable of hitting the US mainland with a nuclear warhead.
Pyongyang has rapidly expanded its facilities for enriching uranium and plutonium production in recent years, Amano told the Journal, expressing doubt over the potential for a diplomatic solution.
During his visit to South Korea last week, Tillerson declared Washington would drop the "failed" approach of "strategic patience" with Pyongyang and warned that US military action was possible.
That marked a sharp divergence from China's insistence on a diplomatic approach to its neighbour, which it has long protected.
In January, South Korea said the North had enough plutonium to make 10 nuclear bombs, as well as a "considerable" ability to produce weapons based on highly-enriched uranium.
The North has boosted plutonium supplies by reactivating its once-mothballed nuclear reactor in Yongbyon.