In a move that could tip the balance of the Ukrainian conflict in favor of the Russian-backed separatists, Russia is sending a unit of advanced interceptor fighters to an airbase close to the Ukrainian border. Operating from there, the Mig-31 fighter jets would be able to survey airspace well inside Ukraine without actually flying over the country, and alert separatists on the ground of any movements by Ukrainian airplanes.

The National Security and Defense Council of Ukraine tweeted on Wednesday that Russia was moving “Mig-31 fighter jets” to the border.

The Mikoyan Mig-31 is one of the most formidable fighters in the Russian inventory. It’s a large, extremely fast interceptor that can fly at high altitude and almost at three times the speed of sound, making it the fastest aircraft currently in service anywhere. But its usefulness in the Ukrainian conflict would lie in its radar, which can spot as many as 24 aircraft simultaneously from as far as 200 km (125 mi). It can then fire long-range missiles which can hit at a range of 160 km (100 mi). That gives the Foxhound, as it’s known to NATO under a system of code names dating to the Cold War, the ability to see and hit well inside Ukrainian airspace.

Russia hasn’t confirmed that it’s moving any of its about 250 Foxhounds to Millerovo, or anywhere for that matter.

The location of the Millerovo airbase (red dot) on the eastern border of Ukraine. Google Maps

What is known at this point is that a spokesman from the National Security and Defense Council of Ukraine, Andriy Lisenko, said at a press briefing that an aviation unit based in Perm, Russia, was being transferred to Millerovo, a Russian air base just 25 km (15 mi) from the border with the separatist region of eastern Ukraine.

According to the Russian Military Reform blog, run by Dmitry Gorenburg, a senior research scientist at CAN Analysis & Solutions who specializes in Russian defense issues, the only aircraft based at Perm were Mig-31s. Orenburg could not confirm that his data, from 2011, was still accurate, but a Google Maps image of the Perm airbase showed only Mig-31s parked there.

MiG-31 Perm
A contrast-enhanced satellite image of the Perm airbase in Russia, showing Mig-31 fighters parked. Google Maps

Pro-Russian separatists in eastern Ukraine have shot down several Ukrainian air force planes since hostilities began earlier this year, but all with missiles launched from the ground. None were hit by other planes; the rebels are not known to possess any armed aircraft.