Powerful explosions have rocked a Russian air base in Crimea and sent towering clouds of smoke over the landscape in what may mark an escalation of the war in Ukraine.

At least one person was killed and several others were wounded at the Saki base on the Black Sea, authorities said.

Russia’s Defence Ministry denied the base had been shelled and said munitions had blown up, but Ukrainian social networks were abuzz with speculation that it was hit by Ukrainian-fired long-range missiles.

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Rising smoke can be seen from the beach at Saky (UGC/AP)

Videos posted on social networks showed sunbathers on nearby beaches fleeing as huge flames and pillars of smoke rose over the horizon from multiple points, accompanied by loud booms.

Crimea Today News said witnesses reported fire on a runway and damage to nearby homes as a result of what it said were dozens of blasts.

Russia’s state news agency Tass quoted an unidentified ministry source as saying the explosions’ primary cause appeared to be a “violation of fire safety requirements”. The ministry said no warplanes were damaged.

Ukraine’s Defence Ministry said sarcastically on Facebook: “The Ministry of Defence of Ukraine cannot establish the cause of the fire, but once again recalls the rules of fire safety and the prohibition of smoking in unspecified places.”

A presidential adviser, Oleksiy Arestovych, said in his regular online interview that the blasts were caused either by a Ukrainian-made long-range weapon or were the work of partisans operating in Crimea.

During the war, Russia has reported numerous fires and explosions at munitions storage sites in its territory near the Ukrainian border, blaming some of them on Ukrainian strikes.

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The aftermath of an explosion at the headquarters of Russia’s Black Sea Fleet in Sevastopol (Mikhail Razvozhaev/AP)

If Ukrainian forces were responsible for the blasts at the air base, it would be the first known major attack on a Russian military site on the Crimean peninsula, which the Kremlin annexed in 2014.

A smaller explosion last month at the headquarters of Russia’s Black Sea Fleet in the Crimean port of Sevastopol was blamed on Ukrainian saboteurs using a makeshift drone.

Russian planes have used the Saki base to strike areas in Ukraine’s south on short notice.

One person was killed, said Crimea’s regional leader, Sergei Aksyonov. Health authorities said nine people were wounded, one of whom remained in hospital. Others were treated for cuts from shards of glass and released.

Officials in Moscow have long warned Ukraine that any attack on Crimea would trigger massive retaliation, including strikes on “decision-making centres” in Kyiv.

Ukrainian President Volodymyr Zelensky said on Tuesday in his nightly video address: “This Russian war against Ukraine and against all of free Europe began with Crimea and must end with Crimea — its liberation.

“Today it is impossible to say when this will happen. But we are constantly adding the necessary components to the formula for the liberation of Crimea.”

Earlier on Tuesday, Ukrainian officials reported at least three Ukrainian civilians were killed and 23 wounded by Russian shelling in 24 hours, including an attack not far from the Russian-occupied Zaporizhzhia nuclear power plant.

The Russians fired more than 120 rockets at the town of Nikopol, across the Dnipro river from the plant, Dnipropetrovsk governor Valentyn Reznichenko said.

Several apartment buildings and industrial sites were damaged, he said.

Ukraine and Russia have accused each other of shelling Europe’s biggest nuclear plant, stoking international fears of a catastrophe.

The governor of the region where the plant is situated, Oleksandr Starukh, said on Tuesday that radiation levels were normal, but he warned that an accident could spread radiation whichever way the wind blows, carrying it to Moscow and other Russian cities.