(CNN) Four Russia-based nuclear monitoring stations that monitor radioactive particles in the atmosphere have mysteriously gone quiet after an August 8 explosion at a Russian missile testing facility, an explosion that has sparked confusion and concerns about possible increases in radiation levels, according to the Comprehensive Nuclear-Test-Ban Treaty Organization.
CTBTO is an independent body which watches for nuclear weapons testing violations with over 300 monitoring stations around the world. Both Russia and the US are signatories to the treaty.
The two Russian radionuclide stations, called Dubna and Kirov, stopped transmitting data within two days of the explosion, the organization said.
"According to our routine global procedure, the CTBTO contacted the Station Operators as soon as the problems started. They have reported communication and network issues, and we're awaiting further reports on when the stations and/or the communication system will be restored to full functionality," a spokesperson said.
In addition, a senior CTBTO official tells CNN that stations in Bilibino and Zalesovo went silent on August 13.
"Experts continue to reach out to our collaborators in Russia to resume station operations as expediently as possible," the official said.
The organization has 80 radionuclide stations around the globe which "measure the atmosphere for radioactive particles," it says, adding that "only these measurements can give a clear indication as to whether an explosion detected by the other methods was actually nuclear or not."
US officials believe the deadly explosion was caused during testing of the nuclear propelled Russian missile SSC-X-9 which NATO has designated the code name of "Skyfall."
The missile is believed to use a nuclear reactor to help power its flight, giving it the ability to fly for longer periods than a conventional missile.
The explosion at the missile site, which resulted in the death of five Russian military scientists, has been the subject of intense speculation as Moscow has provided few details about the incident, with the Kremlin only saying that "accidents happen."
The mysterious disruption to the radionuclide stations, which track radioactive particles in the atmosphere, comes as Russian officials have given contrasting accounts about the level of radiation released in the explosion.
Local authorities reported a brief spike in radiation following the incident but Russia's Defense Ministry said radiation levels were normal.
Russian authorities also called off the evacuation of a village in northern Russia near the site of the suspected failed missile test, Russian state news agency TASS reported last week.
Last week, the Norwegian Radiation and Nuclear Safety Authority said that "tiny amounts of radioactive iodine" had been detected at an air-filter station, one week after the mystery-shrouded explosion.
President Donald Trump said on Twitter last week that the US "is learning much from the failed missile explosion in Russia," adding, "the Russian 'Skyfall' explosion has people worried about the air around the facility, and far beyond. Not good!"
Russian President Vladimir Putin said Monday that there is no risk of increased radiation levels.
"There is no threat here, no increase in the [radiation] background exists either," Putin said ahead of a meeting with French President Emmanuel Macron at Fort of Brégançon in France.
"We don't see any serious changes there, but preventive measures are being taken so there are no surprises," Putin said, adding that independent experts were sent to the site to monitor the situation.
This story has been updated.