Four Russian radiation monitoring stations went offline following reports of a nuclear accident in Arkhangelsk region on Russia’s northern frontier, fuelling concerns of a cover-up.

The Russian government has been vague and at times contradictory when addressing the mysterious explosion near a military test range on August 8.

At least five nuclear scientists died, and a brief radiation spike was detected over nearby Severodvinsk.

According to the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO), which operates an international network of radiation monitoring stations, two key Russian stations went offline two days after the unexplained explosion and reports of radiation spikes.

According to Russian officials, RBC reported, the stations in Dubna and Kirov experienced “network and communications problems” two days after the explosion in Arkhangelsk region.

Two more detection stations in Bilibino and Zalesovo also went quiet on Aug 13, the Wall Street Journal reported on Monday.

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The Russian military has denied that any radiation was released by the explosion, and an official statement from Severodvinsk authorities notifying the public of an increase in radiation levels was quietly withdrawn from the city government’s website.

International confirmation of a radiation spike is hard to come by.

CTBTO head Lassina Zerbo wrote on Twitter Sunday that the organisation was addressing with station operators “technical problems experienced at two neighboring stations.”

He included a graphic of the organisation's modelling of radioactive particle dispersal over time.

The graphic included time stamps indicating where CTBTO models predicted radioactive particles would travel.

Antennas of a testing facility for seismic and infrasound technologies of the Comprehensive Nuclear-Test-Ban Treaty Organization credit: REUTERS/Leonhard Foeger/File Photo

According to this model, when the two Russian stations stopped reporting, the particles would have been passing directly overhead.

Some have speculated that the blast was caused by a failed test of a nuclear-powered cruise missile.

However, evidence suggests that whatever radiation was released by the August 8th explosion was localised and small scale. Experts say a nuclear-powered cruise missile would release far more.

“When the US deliberately blew apart a nuclear rocket engine at the Nevada Test side in 1965 to see what would happen, the peak gamma dose rate 25 km downwind was 700 microSieverts per hour - hundreds of times greater than what was observed in Severodvinsk,” Edwin Lyman, director of the Nuclear Safety Project at the Union of Concerned Scientists said.