ODESA, Ukraine — A series of explosions rocked a key Russian air base in Kremlin-occupied Crimea on Tuesday, killing at least one person and sowing confusion among local officials about the cause and whether Ukraine’s military could threaten targets on the peninsula.
Publicly, Ukrainian officials would not confirm the involvement of Ukraine’s military, as Russian and occupation officials scrambled to determine the source of the blasts, raising the terrorist threat level in the area. But a senior Ukrainian military official with knowledge of the situation said that Ukrainian forces were responsible, having carried out an attack on the Saki air base on the western coast of Crimea.
Speaking on condition of anonymity to discuss sensitive military matters, the official said the air base was one from which planes regularly took off for attacks on Ukrainian forces. The official would not disclose what type of weapon caused the explosions, saying only that “a device exclusively of Ukrainian manufacture was used.”
A Ukrainian attack on Russian forces in the Crimean Peninsula would represent a significant expansion of Ukraine’s offensive efforts, which had mostly been confined to pushing Russian troops from territories occupied after Feb. 24, when the invasion began. For weeks, however, Ukraine has been shifting troops and striking deeper behind the front lines than before, as it signals that it is preparing a major counteroffensive in the Kherson region and uses longer-range weapons supplied by the West.
Crimea, shielded by the Russian Navy and heavily fortified after eight years in Russian control, has largely been spared the violence. Last month, a small explosive device delivered by drone blew up at the headquarters of Russia’s Black Sea Fleet in the Crimean port of Sevastopol, injuring six but causing little damage. Russia blamed Ukrainian forces for the attack, but Ukrainian officials vociferously denied it.
A strike in Crimea would also be an embarrassment for President Vladimir V. Putin of Russia, who often speaks of Crimea, which he illegally annexed from Ukraine in 2014, as if it were hallowed ground. Ukraine possesses few weapons that can reach the peninsula, aside from aircraft that would risk being shot down immediately by Russia’s heavy air defenses in the region. The air base, which is near the city of Novofederivka, is well over 100 miles from the nearest Ukrainian military position.
The senior Ukrainian official said the attack involved partisan resistance forces loyal to the government in Kyiv, but he would not disclose whether those forces carried out the attack or assisted regular Ukrainian military units in targeting the base, as has sometimes occurred in other occupied Ukrainian territories. It was not clear how many detonations there were, but witnesses and Russian officials cited multiple blasts, which videos posted to social media appeared to confirm.
As with past explosions and fires in occupied territory or within Russian borders, Ukrainian officials made no public admissions, but hinted at involvement.
Ukraine’s Defense Ministry said in a statement that it could not “determine the cause of the explosion,” and suggested that personnel at the base adhere to no-smoking regulations. It then tweeted, with a photo of black smoke rising over the peninsula, “the presence of occupying troops on the territory of Ukrainian Crimea is not compatible with the high tourist season.”
Mykhailo Podolyak, a senior adviser to President Volodymyr Zelensky, was similarly indirect. “The future of the Crimea is to be a pearl of the Black Sea, a national park with unique nature and a world resort, not a military base for terrorists,” he said on Twitter. “It is just the beginning.”
Russia’s Defense Ministry said in a statement that the explosions were caused by the detonation of aviation ordnance at the base. While the ministry offered no speculation about whether Ukrainian forces might have been involved, the decision by Crimea’s Kremlin-installed leader, Sergei Aksyonov, to raise the terrorist threat level to yellow suggested officials were concerned about security on the peninsula.
“This measure is exclusively prophylactic, because the situation in the region is under full control,” Mr. Aksyonov said in a statement on Telegram.
In the eight years of Russia’s occupation of Crimea, the peninsula has transformed from a quiet southern Ukrainian beach destination into a major base of Russian military operations. It is from there that the Kremlin’s forces lunged into southern Ukraine in a lighting operation after Feb. 24 that gobbled up a huge swath of territory, including the neighboring Kherson region, which Russian forces almost fully control.
Shortly after the explosions, Mr. Aksyonov arrived at the scene. Standing in front of a large black plume of smoke, he said that a three-mile perimeter had been erected around the site of the base to protect residents.
“Unfortunately, one person died,” he said. “I express my most sincere sympathies to family and friends.” Crimea’s health ministry reported that at least nine people were injured.
To reach targets deep behind enemy lines, Ukraine has increasingly turned to partisans, often residents of Russian-occupied territories who are loyal to Ukraine, officials said. Such people have helped Ukraine’s military strike Russian bases and ammunition depots, Ukrainian officials say.
Others have carried out attacks themselves. Over the weekend, the Kremlin-installed mayor of the city of Kherson suddenly fell ill and had to be evacuated to Moscow, where there were reports that he was in a coma. Less than 24 hours later, the deputy head of a major town in the region was shot and killed at his home, a spokeswoman for the region said.
The senior Ukrainian official said that both instances were the work of local partisan forces, though his claim could not be independently verified.
In May, an explosion in Melitopol, an occupied city northeast of Crimea, appeared to target — and miss — the regional chief installed by Moscow.
Since the invasion began, Russia has periodically suffered attacks within its own borders, including a helicopter assault on a fuel depot and fires at another fuel depot — both sites relatively close to Ukrainian territory — and a blaze much deeper into Russia, at a military research institute in Tver, near Moscow.
Russia accused Ukraine of carrying out the helicopter strike, and analysts have suggested that Ukrainian sabotage was probably behind the fires. But Ukrainian officials have only indirectly suggested any involvement, and declined to publicly confirm it.
In its initial statement about the explosions in Crimea on Tuesday, Russia’s Defense Ministry said that there was no damage and that no one was injured, a claim that was quickly contradicted.
The detonations and Moscow’s scramble to explain them recalled the sinking of the flagship of Russia’s Black Sea fleet in April. After an explosion on the ship, the Moskva, Ukraine quickly announced that it struck the ship with Neptune missiles, an account U.S. officials later backed up. Russia said an accidental fire ignited an ammunition store, and said the next day that Moskva was lost in stormy conditions as it was being towed to port, though video that appeared to show the sinking ship showed mild weather and calm seas.
Russia’s Defense Ministry said that the crew of at least 510 men was evacuated, and later acknowledged that one was killed and 27 were missing; Russian news outlets operating outside the country put the toll at about 40. Families of crew members challenged official silence about the fate of their sons, and some said they had been given conflicting accounts.
Also like the sinking of the Moskva, which was once an emblem of Russian dominance in the Black Sea, a strike on a military target on Crimea would have a symbolic weight for both Ukraine and Russia. The peninsula has served not only as a launching pad for the invasion in southern Ukraine, but a hub for Russian military operations in the region, home to Russian Navy ships blockading Ukrainian ports, and a base for engineers to restore roads, rails and a critical freshwater canal in order to cement Russia’s grip on occupied territories.
The Kremlin has pushed Crimea as a patriotic vacation spot, a haven for wealthy Russians no longer welcome abroad, and a feature of Russia’s new schooling for young students. And Mr. Putin, who has repeatedly visited since 2014, has made a yearly event out of celebrating the anniversary of annexation, with speeches, concerts and forests of Russian flags.