Russia is massing troops and hundreds of pieces of heavy military equipment, such as tanks and artillery, along Ukraine's border. That's according to Reuters reporter Maria Tsvetkova, who saw and took photos of the deployments on Wednesday. The same day, NATO Secretary General Jens Stoltenberg told a think tank audience in Washington that Russia had deployed 250 aircraft and 700 pieces of heavy military equipment to the Ukrainian border as part of a military exercise.

Is this the start of another Russian invasion of Ukraine? Disturbingly, Tsvetkova reports that "many of the vehicles have number plates and identifying marks removed while many of the servicemen had taken insignia off their fatigues."

Russian tanks and troops that have previously been used to invade Ukraine — an invasion Moscow does not acknowledge — have similarly removed signifying marks. It's difficult to imagine another reason to do this. Tsvetkova also notes that the road from the military base to the nearby Ukrainian border had been recently repaired.

In August, Russian troops and tanks unofficially invaded eastern Ukraine to bolster pro-Russia separatists who had been losing ground against the Ukrainian army. While the conflict in eastern Ukraine is currently on ceasefire, there are fears that Russia may use the pause in fighting to build up separatist forces, or even to launch an offensive breaking the ceasefire.

However, it is also possible that the Russian military exercises are not preparation for an invasion, but rather an act meant to intimidate and bully Ukraine. As the Wall Street Journal's Julian Barnes wrote, "U.S. officials have said such surprise exercises are being used to destabilize the government of Ukraine." Moscow may be hoping to pressure Ukraine's government to concede better political terms over the ceasefire. Stoltenberg, it is worth noting, did not accuse Russia of using the exercise as a cover for an impending invasion.

Removing insignias and markings from the tanks and troops could, in this reading, be an act of psychological warfare meant to threaten Ukraine by creating confusion as to whether Russia could once more invade. This unknowability is precisely what makes Russian provocations so destabilizing and, in their own way, effective. Ukraine's leaders are in this way trapped within what the journalist Peter Pomerantsev termed the Kremlin Hall of Mirrors.