An explosion rocked a secretive Russian nuclear test site inside the Arctic Circle last week. At first, Russian officials denied that the blast produced any radioactive activity. They also denied any evacuations would be needed. 

But then authorities in a village near the explosion advised locals to vacate the town for several hours on Wednesday. Greenpeace reported that background levels of radiation in the area had spiked to 20 times normal levels. And the explosion killed at least five people, with Russia’s state atomic energy corporation finally admitting it occurred at a small nuclear reactor. 

The incident is the second time in two months that the Kremlin has kept a tight seal on information on disasters involving nuclear projects ― a fire aboard one of the nation’s nuclear submarines killed 14 sailors in early July. The incidents have fueled speculation about Russia’s military activities and raised alarm among arms control experts, who are concerned by the secretiveness displayed by one of the world’s premier nuclear powers about mishaps with humanity-threatening technology. 

Luckily, international protocols have evolved significantly since 1986′s infamous disaster at Chernobyl, which the Soviet Union tried to minimise until widespread radiation spikes and international measurements destroyed the government’s cover story. 

“It’s not like the 1980s when Chernobyl exploded and there was this really long gap,” said Jeffrey Lewis, director of the East Asia Non-Proliferation Program at the Middlebury Institute of International Studies in Vermont. “It would be extremely, extremely hard to hide a nuclear disaster today.”

The new fatal blast is believed to have happened at theNyonoksa test range in northern Russia on August 8and involved a failed test of a nuclear-powered “Burevestnik” cruise missile designed to evade missile defence systems and reach anywhere in the world, according to US officials and nuclear experts. 

Thanks to technological safeguards against undisclosed nuclear releases, the reality of the accident was almost immediately apparent. The Comprehensive Nuclear Test Ban Treaty Organisation, for example, maintains sensor stations across the globe monitoring radionuclides for spikes in radiation levels. It also has methods of measuring sound waves and seismic activity to detect clandestine nuclear tests.

Monitors also check social media after a nuclear event for information, Lewis said, including the accounts of the scientists or armed forces who are reported to have been killed. Extensive satellite imagery can look at the area around reported nuclear tests and organizations check open-source data for any movements related to an event. 

Lewis and his team, for instance, quickly found that a Russian ship used for nuclear fuel transport was in the area of the test site when last week’s explosion took place.

More information on just how much radiation the blast released is expected to come out in the next few days. 

Aside from these technological monitors, governments are supposed to use diplomatic channels to notify the global community about accidents ― though Russia has taken advantage of some loopholes in these agreements.

The Convention on Early Notification of a Nuclear Accident, ratified following the Chernobyl disaster, makes it obligatory for states to extensively report the release of radioactive material or the potential for it to be released, such as when Mexico lost a truck full of radioactive medical material in 2013. But the treaty does not have the same mandatory reporting rules for military nuclear projects, and states are far more hesitant to disclose information on nuclear weapons programs.  

Radiation releases from “a hospital source for cancer treatment is one thing and a developmental secret weapon is quite another,” said Cheryl Rofer, a retired scientist at the Los Alamos National Laboratory in New Mexico and nuclear expert.“Russia certainly has not been very forthcoming on this latest accident.” 

It appeared to stonewall the International Atomic Energy Agency, which contacted the Russian government about last week’s explosion but got a comically sparse explanation. An IAEA spokesperson told HuffPost that Russian officials replied only that radiation levels were normal in the area and “this facility does not belong to the facilities for the peaceful use of nuclear energy.” 

The Kremlin’s repeated celebration its purported missile advancements is a likely reason for its sensitivity about the accident.

Russian President Vladimir Putin showed a video simulation last year of the “Burevestnik” missile’s ability to strike Florida. The country’s missile projects have spurred debate over whether a new arms race will emerge between the U.S., Russia and China. President Donald Trump has done little to dispel that fear, boasting on Monday that the U.S. missile program was superior to its Russian counterpart. 

“The United States is learning much from the failed missile explosion in Russia,” Trump tweeted. “We have similar, though more advanced, technology.“

Diplomatic conditions aimed at creating transparency involving nuclear accidents are likely to deteriorate. Trump’s tweet started a missile-measuring contest between Washington and Moscow, with Putin spokesman Dmitry Peskov claiming on Tuesday that Russia’s missiles surpassed other countries’ capabilities. The US and Russia also have both been walking back from arms control measures as they pursue new military technology.

Trump earlier this month withdrew the U.S. from the Intermediate Nuclear Forces treaty that banned certain types of cruise missile and had been in effect since 1987. The New START treaty, which puts limits on nuclear weapons, is set to expire in 2021 and Trump national security adviser John Bolton has called its renewal “unlikely.”