Satellite images show that Russia’s military moved old anti-aircraft missiles to Ukraine as it faced a shortage of advanced weapons this summer, inflicting heavy damage on civilians as a result, Finland’s Yle broadcaster reported Sunday.

At least four out of 14 anti-aircraft missile bases surrounding St. Petersburg were “emptied of equipment” in August and September, Finnish military expert Marko Eklund was quoted as saying.

“It is most likely that the equipment that has been removed is primarily from the old S-300 system,” Eklund, who has monitored the Russian armed forces for over 20 years, added.

The remaining missiles that protect the airspace over Russia’s second-largest city near the Finnish border appear to be S-400 systems, which have twice the range of their Soviet-era predecessors, the S-300. 

Russia has likely moved some of its oldest equipment toward the Ukrainian battlefield and thus has not significantly weakened St. Petersburg’s air defenses, Eklund said.

Yle estimates the 14 batteries placed in a circle around St. Petersburg include more than 100 mobile firing platforms equipped with at least 450 missiles.

The latest transfer follows similar movements closer to Ukraine in southern Russia’s Voronezh region, where Yle reports half of its missile fleet had “vanished” by May, three months after Moscow launched an unprovoked invasion of its neighbor.

Russia has so far fired more than 500 S-300 missiles on Ukrainian targets and has three years’ worth of missiles remaining, or 7,000 items in total, Ukraine’s defense ministry intelligence chief said earlier this month.

S-300s are not originally intended for ground targets and their use is likely explained by the Russian military’s shortage of conventional ballistic missiles, according to Yle.

“These old missiles are used for ground targets in such a way that the greatest damage seems to be done to civilians,” it quoted Eklund as saying.