North Korea could have enough plutonium and highly enriched uranium by the end of 2016 to build up to 20 nuclear bombs, a leading US nuclear scientist says.

Siegfried Hecker, director from 1986-97 of Los Alamos National Laboratory, the top US government nuclear facility, offered the estimate of the Pyongyang regime's fissile material in an article published this week by the US-Korea Institute at Johns Hopkins University.

He said that the latest North Korean nuclear detonation on September 9, the fifth known test in 10 years, "must be viewed with great concern, not for any specific capabilities it may have demonstrated, but as part of this enormous buildup of North Korea's nuclear arsenal."

The test, in violation of UN Security Council resolutions, brought immediate condemnation and calls for further tightening of economic and political sanctions against the already severely isolated communist regime.

Australia was the latest to endorse tougher actions.

"We see North Korea's provocative acts as not only a threat to the Korean peninsula but to our region and globally," Foreign Minister Julie Bishop told reporters Wednesday in Canberra.

UN Secretary General Ban Ki-moon said he had never seen more heightened tensions on the Korean Peninsula. It is important for the Security Council to take urgent action to prevent further provocative actions by North Korea and to send a strong message to the country's leaders, he said.

Hecker estimates that North Korea could have stockpiled 32 to 54 kilograms of plutonium, plus 300 to 400 kilograms of bomb-grade uranium, before the end of the year. The regime could be producing enough material for about seven more bombs a year moving forward, Hecker said.

A senior fellow and affiliated faculty member at Stanford University's Centre for International Security and Cooperation, Hecker toured North Korean nuclear facilities, most recently in 2010, when international inspections were still ongoing.

"Left unchecked, Pyongyang will likely develop the capability to reach the continental United States with a nuclear-tipped missile in a decade or so," he wrote. "Much more troubling for now is that its recent nuclear and missile successes may give Pyongyang a false sense of confidence and dramatically change regional security dynamics."

Hecker lamented the "death of diplomacy" due to US President Barack Obama's tactic of strategic patience, which has left North Korea "unconstrained by international opprobrium and escalating sanctions."

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