(CNN)At least seven Russian warplanes were destroyed after explosions rocked annexed Crimea on Tuesday, new satellite images show, in what CNN research found could be Moscow’s biggest loss of military aircraft in a single day since World War II.
The destroyed warplanes appear to be Su-24 bombers and Su-30 multirole fighter jets, said Peter Layton, a fellow at the Griffith Asia Institute and a former Australian Air Force pilot, who examined Planet Lab satellite photos showing the Saki Air Base before and after the explosions.
Two more warplanes appear to have been damaged, Layton said. On Wednesday, the Ukrainian armed forces added nine aircraft to the tally of Russian military hardware they say has been destroyed since the Russian invasion of Ukraine began in February.
The Ukrainian Ministry of Defense said it could not determine the cause of the explosions at the air base, which lies 225 kilometers (140 miles) behind the Russian front line, according to the Institute for the Study of War think tank.
The Russian Ministry of Defense said the blasts were caused by aviation ammunition — but did not say how it had been detonated.
Video on social media, verified and geolocated by CNN as being from the air base, shows smoke rising from the base before it is rocked by three large, fiery explosions that send black mushroom clouds into the sky. Two of the explosions happen almost simultaneously and a third occurs shortly thereafter.
The satellite photos also show the explosions burned a swath of vegetation around a portion of the air base.
Layton said the satellite images point to a deliberate attack, rather than an accident, due to the presence of three large craters.
Whatever caused the craters could have caused other Russian munitions to explode, Layton said.
“If one bomb explodes, it can send high speed, very hot fragments into any adjacent bombs and detonate them. This is called explosive propagation,” Layton said. “In the image of the Russian air base, you can see three explosion sources. These set off adjacent aircraft that it seems had bombs on them. The explosion propagated.”
Russian munitions are not engineered to avoid such chain-reaction explosions, Layton added.
He noted that the type of destruction at the air base is reminiscent of what led to the sinking of the Russian Navy cruiser Moskva earlier in the Ukraine war.
“The Moskva also had an internal explosion when warheads in the anti-ship cruise missiles on board self-detonated,” Layton said. “This was the explosive fill burning to explosion.
“Russian weapons are less safe than Western weapons in terms of the sensitivity of the explosive fill of the warheads. This is at least due to most weapons being old ex-Soviet stocks and so old technology,” he said.
The Planet Labs photos show that other aircraft not destroyed but possibly damaged by the explosions had been moved away from the area where the blasts occurred.
The detonations also caused damage in a nearby town, where windows in some buildings were blown out, according to Russian state news agency TASS. Some high-rise buildings lost power, while shops and a cultural center were damaged, TASS reported.
Four helicopters and a four-engine plane appear to have left the air base in the past 24 hours, the satellite images taken before and after the attack appear to show.
Since 2014, the Saki Air Base has been home to a Russian naval aviation regiment, part of Russia’s Black Sea Fleet, according to the state-run RIA-Novosti news service.
Russia annexed Crimea from Ukraine in 2014, after Russian President Vladimir Putin sent military forces into what was then an autonomous region of southern Ukraine with strong Russian loyalties.
Thousands of Russian-speaking troops wearing unmarked uniforms poured into the peninsula in early March that year. Two weeks later, Russia completed its annexation of Crimea in a referendum slammed by Ukraine and most of the world as illegitimate.
On Tuesday, Ukrainian President Volodymyr Zelensky said the war “began with Crimea and must end with Crimea — its liberation.”
The number of planes destroyed at the base likely mark Tuesday as one of the most destructive days for Russian military aviation in more than seven decades, including the Soviet era.
A CNN examination of the little available data on military aircraft losses during Soviet times and in modern Russia do not indicate such a substantial toll from one incident in a single day.
The explosions killed at least one person, and injured at least nine, according to a statement from the Crimea Health Ministry.