The Russian military admitted that a bomb fired by one of its jets inadvertently created a strong blast in a Russian city close to the Ukrainian border, injuring two people and frightening others.

During Russia’s ongoing military action in Ukraine, drone attacks have been frequent in Belgorod, a city of 340,000 people situated roughly 40 kilometers (25 miles) east of the Russia-Ukraine border. The Ukrainian military resisted making a public claim of responsibility for the attacks, although Russian officials still accused it of carrying out the earlier attacks. The late-night explosion on Thursday was far more powerful than anything the citizens of Belgorod had ever witnessed. Witnesses heard a low hissing sound, then a blast that shattered windows in surrounding apartment buildings and caused the structures to shake.

“At around 22:15 Moscow time on April 20, when a Su-34 plane of the Russian Aerospace Forces was performing a flight above the city of Belgorod, an emergency release of an air ordnance occurred,” the Russian Defense Ministry, per Russian state media, Tass said.

It destroyed many automobiles, threw one into a store roof, and left a 20-meter-wide crater in the center of a tree-lined avenue surrounded by apartment buildings. Authorities reported that two people were hurt, while a third was later admitted to the hospital with hypertension. Russian analysts and military bloggers were buzzing with hypotheses about what weapon Ukraine had used for the attack as soon as the explosion occurred. Many of them demanded severe retaliation.

But about an hour later, the Russian Defense Ministry admitted that the explosion was caused by a weapon that one of its own Su-34 bombers unintentionally discharged. The ministry gave no other information, but according to military analysts, the device was probably a potent 1,100-pound bomb. Russian pundits questioned the warplane’s decision to fly over Belgorod and urged the military to refrain from future risky overflights.

Some claimed that the bomb that was unintentionally dropped on Belgorod may have been one of a group of modified weapons that can glide to targets hundreds of miles away thanks to their wings and GPS-guided targeting systems. Such gliding bombs have just lately been employed by the Russian air force, and some experts believe they may be prone to malfunctions.