ODESA, Ukraine — To reach targets deep behind enemy lines, the Ukrainian military is believed to be turning to residents of Russian-occupied territories who are loyal to Ukraine.
The shadowy fighters, also known as partisans, have been credited with a series of recent mysterious attacks: the sickening of the Kremlin-installed mayor of the city of Kherson who had to be evacuated to Moscow over the weekend; the deadly shooting of the deputy head of another major town in the region less than 24 hours later; and a series of explosions at a Russian air base on the Kremlin-occupied Crimean Peninsula on Tuesday.
As Russian and occupation officials scrambled to determine the cause of Tuesday’s attack, which killed one person, a senior Ukrainian military official with knowledge of the situation said that Ukrainian forces were behind the blast at the Saki Air Base on the western coast of Crimea.
“This was an air base from which planes regularly took off for attacks against our forces in the southern theater,” the official said, speaking on the condition of anonymity to discuss sensitive military matters. The official would not disclose the type of weapon used in the attack, 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 until now have been largely limited to pushing Russian troops back from territories occupied after Feb. 24, when the invasion began.
It 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 nearly 200 miles from the nearest Ukrainian military position.
Videos verified and reviewed by The New York Times show that a plume of smoke was rising from the air base just before at least three explosions: two in quick succession and a third a few moments later. It is unclear from the videos what caused the blasts. In addition, a video uploaded to social media shows at least one warplane, an Su-24M, destroyed on the tarmac at the base.
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 Russian-occupied territories.
To reach targets deep behind enemy lines, Ukraine has increasingly turned to guerrillas in Russian-occupied territories, officials said. Partisans have, for instance, helped Ukrainian forces target Russian bases and ammunition depots in the Kherson Region, Ukrainian officials say.
Publicly, Ukrainian officials on Tuesday would not confirm the involvement of Ukraine’s military. 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.
Other officials did not exactly deny that Ukraine was behind the explosion.
“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,” Mykhailo Podolyak, a senior adviser to President Volodymyr Zelensky of Ukraine, said in a tweet. “It is just the beginning.”
In his nightly speech, Mr. Zelensky did not address whether Ukraine was behind the Crimea attack, but he did say, “Crimea is Ukrainian, and we will never give it up,” adding as he signed off that the world should “support the Armed Forces of Ukraine, our intelligence and everyone who is fighting to liberate our land and repel the Russian colonial invasion.”
Russia’s Defense Ministry said in a statement that the explosion was caused by the detonation of stockpiled ordnance for warplanes 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 that 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.
Christiaan Triebert contributed reporting.