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.