Moscow — When a powerful blast shook a Russian city near the border of Ukraine residents thought it was a Ukrainian attack. But the Russian military quickly acknowledged that it was a bomb accidentally dropped by one of its own warplanes.

Belgorod, a city of 340,000 about 25 miles east of the border with Ukraine, has faced regular drone attacks that Russian authorities blame on the Ukrainian military, but the explosion late Thursday was far more powerful than anything its residents had heard before.

Witnesses reported a low hissing sound followed by a blast that made nearby apartment buildings tremble and threw a car on a store roof. 

It left a 66-foot-wide crater in the middle of a tree-lined boulevard flanked by apartment buildings, shattering their windows, damaging several cars and injuring two residents. A third person was later hospitalized with hypertension.

Immediately after the explosion, Russian commentators and military bloggers were abuzz with theories about what weapon Ukraine had used for the attack. Many called for a powerful retribution. But about an hour later, the Russian Defense Ministry acknowledged that the explosion was caused by a weapon accidentally dropped by one of its own Su-34 bombers. It didn't offer any further details, but military experts said the weapon likely was a powerful 1,100-pound bomb.

In Thursday's blast, the weapon was apparently set to explode with a small delay after impact, to hit underground facilities.

Belgorod Gov. Vyacheslav Gladkov said local authorities decided to temporarily resettle residents of a nine-story apartment building near the blast while it was inspected to make sure it hadn't suffered irreparable structural damage.

The explosion in Belgorod followed the crash of a Russian warplane next to a residential building in the port city of Yeysk on the Sea of Azov that killed 15 people. Yeysk hosts a big Russian air base with warplanes flying missions over Ukraine.

Military experts have noted that as the number of Russian military flights have increased sharply during the fighting, so have the crashes and accidents.

Analysts and U.S. officials have described Russia's tactics in the Ukraine war as akin to the methods applied by the armies on both sides of the First World War, as Moscow has thrown wave after wave of both man and machine at the front lines for months, rapidly depleting its resources with little to show in return. 

Last month it emerged that the Russian military was rolling Soviet-era tanks off storage bases where they had been mothballed for decades, presumably to bolster its forces amid the wanton destruction of its hardware on the battlefield.

Ukraine has also relied heavily on its stocks of old Soviet-era tanks and other weapons during the war, but it has begun to take delivery of dozens of modern battle tanks promised by its European partners, with U.S. tanks also expected to arrive this year. 

In March, Poland said it would also give Ukraine about a dozen MiG-29 fighter jets, becoming the first NATO member to fulfill Kyiv's increasingly urgent requests for warplanes to defend itself against the Russian invasion.

In:
• War
• Ukraine
• Russia
• Vladimir Putin