British officials reportedly suspect that North Korea was able to develop its nuclear arsenal quicker than expected due to help from Iran and possibly Russia.

“It is not credible that North Korean scientists alone brought about the technological advances,” government sources told the UK’s Sunday Telegraph.

The sudden surge in technological capability by the Pyongyang regime reportedly points to help from elsewhere.

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“North Korean scientists are people of some ability, but clearly they’re not doing it entirely in a vacuum,” an unnamed government minister told the paper.

British authorities suspect that Iran has offered behind-the-scenes technological assistance for Pyongyang’s nuclear program, though others think that Russia may have provided some of the know-how.

“There is currently an investigation into exactly how the country has managed to make this leap in technological ability,” UK Foreign Secretary Boris Johnson said last week. “We are looking at the possible role that may have been played, inadvertently or otherwise, by some current and former nuclear states.”

North Korean carried out its sixth nuclear test last week, and South Korea has voiced fears that it may test a ballistic missile in the coming days.

NATO Secretary General Jens Stoltenberg said Sunday that North Korea’s nuclear and missile program represented a “global threat and requires a global response,” though he refused to say whether an attack on the Pacific US territory of Guam would trigger the military alliance’s collective defense clause.

“The reckless behavior of North Korea is a global threat and requires a global response, and that of course also includes NATO,”

told the BBC’s “The Andrew Marr Show.”

“We call on Korea to abandon its nuclear programs, it’s missile programs, and to refrain from more testing, because this is a blatant violation of several UN security resolutions and it’s a threat to international peace and stability.”

Asked whether a strike against Guam would be covered under the clause that commits NATO members to come to the defense of each other, he said: “I will not speculate about whether Article Five will be applied in such a situation. What I will say is we are now totally focused on how can we contribute to a peaceful solution of the conflict.”

German Chancellor Angela Mergel voiced support for a diplomatic push to end North Korean nuclear weapons and missile development along the lines of a past deal with Iran.

“I would say yes immediately if we were asked to join talks,” Merkel told weekly newspaper Frankfurter Allgemeine Sonntagszeitung.

Talks between Iran and six world powers, sealed with a 2015 deal for Tehran to roll back its nuclear program and submit to inspections in exchange for some sanctions being rolled back, were “a long but important period of diplomacy” that had achieved a “good end,” she added.

“I could imagine such a format for the settlement of the North Korea conflict. Europe and especially Germany ought to be ready to make a very active contribution,” Merkel said.