Satellite images appear to show at least seven fighter planes at an airbase in Crimea have been blown up after an apparent Ukrainian attack on the base.
Ukraine said on Wednesday that nine Russian warplanes were destroyed in a string of explosions that appeared to be the result of a Ukrainian attack, which would represent a significant escalation in the war.
Russia denied any aircraft were damaged in Tuesday's blasts — or that any attack took place.
But satellite photos showed at least seven fighter planes at the base had been blown up and others probably damaged.
Ukrainian officials stopped short of publicly claiming responsibility for the explosions while mocking Russia's explanation that a careless smoker might have caused ammunition at the Saky air base to catch fire and blow up.
Analysts also said that the explanation does not make sense and that the Ukrainians could have used anti-ship missiles to strike the base.
If Ukrainian forces were, in fact, responsible for the blasts, it would be the first known major attack on a Russian military site on the Crimean Peninsula, which was seized from Ukraine by the Kremlin in 2014. Russian warplanes have used Saky to strike areas in Ukraine's south.
Crimea holds huge strategic and symbolic significance for both sides. The Kremlin's demand that Ukraine recognises Crimea as part of Russia has been one of its key conditions for ending the fighting, while Ukraine has vowed to drive the Russians from the peninsula and all other occupied territories.
The explosions, which killed one person and wounded 14, sent tourists fleeing in panic as plumes of smoke rose over the coastline nearby. The video showed shattered windows and holes in the brickwork of some buildings.
One tourist, Natalia Lipovaya, said that "the earth was gone from under my feet" after the powerful blasts.
Sergey Milochinsky, a local resident, recalled hearing a roar and seeing a mushroom cloud from his window. "Everything began to fall around, collapse," he said.
Crimea's regional leader, Sergei Aksyonov, said some 250 residents were moved to temporary housing after dozens of apartment buildings were damaged.
Russian authorities sought to downplay the explosions, saying on Wednesday that all hotels and beaches were unaffected on the peninsula, which is a popular tourist destination for many Russians.
But a video posted on social media showed long lines of slowly moving cars on the road to Russia as tourists headed for home.
A Ukrainian presidential adviser, Oleksiy Arestovych, cryptically said that the blasts were either caused by Ukrainian-made long-range weapons or the work of Ukrainian guerrillas operating in Crimea.
A Ukrainian parliament member, Oleksandr Zavitnevich, said the airfield was rendered unusable. He reported on Facebook that it housed fighter jets, tactical reconnaissance aircraft and military transport planes.
"Unofficially the military acknowledges that it was a Ukrainian strike"
"Official Kyiv has kept mum about it, but unofficially the military acknowledges that it was a Ukrainian strike," Ukrainian military analyst Oleh Zhdanov said.
The base is at least 125 miles from the closest Ukrainian position. Mr Zhdanov suggested that Ukrainian forces could have struck it with Ukrainian or Western-supplied anti-ship missiles that have the necessary range.
The Washington-based Institute for the Study of War said it could not independently determine what caused the explosions but noted that simultaneous blasts in two places at the base probably rule out an accidental fire but not sabotage or a missile attack.
But it added: "The Kremlin has little incentive to accuse Ukraine of conducting strikes that caused the damage since such strikes would demonstrate the ineffectiveness of Russian air defence systems."
During the war, the Kremlin has reported numerous fires and explosions on Russian territory near the Ukrainian border, blaming some of them on Ukrainian strikes. Ukrainian authorities have mostly kept silent about the incidents.