Explosions and fires ripped through an ammunition depot in Russia-annexed Crimea on Tuesday in theon the peninsula in just over a week, forcing the evacuation of more than 3,000 people.
Russia blamed the blasts in the village of Mayskoye on an "act of sabotage," without naming the perpetrators.
Separately, the Russian business newspaper Kommersant quoted residents as saying plumes of black smoke also rose over an air base in Crimea's Gvardeyskoye.
Ukraine stopped short of publicly claiming responsibility for any of the blasts, including those that destroyed nine Russian planes at another Crimean air base last week. Russia seized Crimea from Ukraine in 2014 and has used it to launch attacks against the country in the war that began nearly six months ago.
In another reported act of sabotage, Russia's Tass news agency quoted the FSB security agency as saying Ukrainian operatives blew up six high-voltage transmission towers earlier this month in Russia's Kursk region, close to Ukraine.
If Ukrainian forces were behind the explosions in Crimea, that would represent a significant escalation in the war. Such attacks could also indicate that Ukrainian operatives are able to penetrate deeply into Russian-occupied territory, supplementing attempts to weaken Moscow's forces on the front lines.
"Frankly, that changes the front across the board," retired U.S. Marine Corps intelligence officer Hal Kempfer told CBS News senior foreign correspondent Charlie D'Agata after the attack last week. "If they can continue the momentum, if they can continue to do deep strikes, if they continue to make gains across the Kherson Oblast, they might be able to push all the way across that southern flank."
That strike drew a quick, brutal response from Russia. President Vladimir Putin's forces retaliated with increased shelling and missile attacks on towns and villages across southern Ukraine.
The Kremlin has demanded that Kyiv recognize Crimea as part of Russia as a condition for ending the fighting, while Ukraine has vowed to drive Moscow's forces from the peninsula on the Black Sea.
Videos posted on social media showed thick columns of smoke rising over raging flames in Mayskoye, and a series of explosions could be heard. The Russian Defense Ministry said the fires damaged a power plant, power lines, railroad tracks and apartment buildings.
"We came out to take a look and saw clouds of smoke coming from the cowshed where the military warehouses are," said resident Maksim Moldovskiy. "We stayed there until about 7-8 a.m. Everything was exploding — flashes, fragments, debris falling on us. Then the emergency guys came and said they were evacuating everybody."
Crimea's regional leader, Sergei Aksyonov, said two people were injured and more than 3,000 evacuated from two villages.
"The detonations are rather strong. Ammunition is strewn all over the ground," he said, adding that several homes burned down.
Crimea is a popular summer destination for Russian tourists, and last week's explosions at Crimea's Saki air base sent sunbathers on beaches fleeing as flames and pillars of smoke rose over the horizon.
Ukrainian officials warned Tuesday that Crimea would not be spared the ravages of war.
Rather than a travel destination, "Crimea occupied by Russians is about warehouse explosions and a high risk of death for invaders and thieves," Ukrainian presidential adviser Mykhailo Podolyak said on Twitter.
Russia blamed last week's explosions on an accidental detonation of munitions, but satellite photos and other evidence — including the dispersed blast sites — pointed to a Ukrainian attack, perhaps with anti-ship missiles, military analysts said.
Britain's Defense Ministry said in an intelligence update that vessels in Russia's Black Sea Fleet are in an "extremely defensive posture" in the waters off Crimea, with ships barely venturing out of sight of the coastline. Russia's flagship Moskva, and last month Ukrainian forces retook strategic Snake Island.
The Russian fleet's "limited effectiveness undermines Russia's overall invasion strategy," the British said. "This means Ukraine can divert resources to press Russian ground forces elsewhere."
Russian Defense Minister Sergei Shoigu charged that in addition to supplying arms to Ukraine, Western allies have provided detailed intelligence and instructors to help Ukraine operate weapons that can hit deep in occupied territory.
"Western intelligence agencies not only have provided target coordinates for launching strikes, but Western specialists also have overseen the input of those data into weapons systems," Shoigu said.
Meanwhile, in the Donbas, the industrial expanse in the east that has been the focus of the fighting in recent months, one civilian was killed in Russian shelling, and two others were wounded, according to the Ukrainian regional governor, Pavlo Kyrylenko.
In Kharkiv in northeastern Ukraine, one civilian was killed and nine others were wounded by Russian shelling, regional Gov. Oleh Syniehubov said. He said the overnight attack was "one of the most massive shellings of Kharkiv in recent days."
One good piece of news emerged from the region: A United Nations-chartered ship loaded with Ukrainian grain set out for the hunger-stricken Horn of Africa in the first such relief delivery of the war. The shipment was made possible by an internationally brokered deal to free up grain trapped in Ukrainian ports by the fighting.
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