The thick plumes of black smoke that swirled over an air base in Crimea sent scores of sun-seekers running from the Russia-occupied peninsula, clogging traffic on the highway leading to the only bridge to their homeland.

Ukrainian officials retweeted the videos of panicked Russian tourists racing for the exits. One assessed that nine Russian fighter jets had been destroyed in the incident on Tuesday evening. But they did not go as far as take credit for the damage inflicted on the Saki Air Base, some 200km from the nearest known Ukrainian position.

“Smoking cigarettes kills,” a senior Ukrainian official wrote in a tongue-in-cheek text soon after the explosions.

The Crimea explosions are the most severe of a run of incidents involving Russian targets behind the front line that western defence analysts suspect have been caused by pro-Ukrainian forces under direct or indirect guidance of Kyiv.

These unclaimed incidents have put the Kremlin in the awkward position of having to deny that they could have been inflicted by Ukraine-friendly groups. Moscow suggested Tuesday’s explosions in Crimea, which it annexed in 2014, might have been accidental, due to the mishandling of ammunition.

“Only violation of the fire safety requirements is seen as the main cause of the explosion of several munitions at the Saki airfield,” an unnamed Russian defence ministry source was quoted as saying by the Interfax news agency.

Coming alongside what appear to be partisan actions against Russian soldiers in recently occupied Ukrainian territories, they are designed to sow unrest and doubt among the Russian population and boost Ukrainian morale, more than make a material difference on the battlefield, analysts and western officials say.

“The mere fact it took place so far behind enemy lines and in Crimea, which [Russian president Vladimir] Putin considers de facto Russian territory, is a real morale boost for Ukraine,” said one European intelligence official. “It also shows that Ukraine has higher capabilities than Russia may have previously thought.”

A western military official said the propaganda gain from the Saki air base explosions was “the combination of a grand slam, a hole-in-one and a last-second goal” all at once.

In the past few months, officials appointed by the Kremlin have been killed in Ukrainian territories seized by Russian forces — some by car bombs, others assassinated by gunshot. The Kremlin-appointed deputy head of the Russia-occupied Kherson province last week denied reports that his boss had been poisoned or had a stroke after he was evacuated to Moscow for treatment.

Infrastructure that is key to Russia’s war effort has also been targeted. A “kamikaze” drone struck a Russian oil refinery in the southern Rostov region in June.

Russia has accused Ukraine of inflicting some of the damage but has refused to confirm many of the incidents. State media has taken to reporting of “bangs”, rather than “explosions”, while officials have explained some of them as safety violations or industrial accidents.

Moscow’s refusal to acknowledge the attacks, analysts say, could be an attempt to prevent panic spreading among locals about Ukraine’s ability to strike within Russia and to maintain the illusion that it is only engaged in a “special operation” and not a full-scale invasion.

However, the explosions at the Saki air base are of a magnitude far greater than any operations Ukraine is suspected of having carried out.

Western military officials and analysts suggested they may have been caused by a Ukrainian-made missile or a group of saboteurs, rather than the less likely scenario of an accident.

A Nato official declined to elaborate on the incident only to say that no weapons provided by the west were used in any assault. The New York Times and the Washington Post reported that Ukrainian special forces, working alongside Ukrainian partisans, were behind the assaults.

Ukrainian forces have previously used domestically developed weaponry — such as the locally manufactured Neptune shore-based missile that sank the Moskva flagship of Russia’s Black Sea fleet in April.

A western defence adviser said that Kyiv had a few late model Grom ballistic missiles with a range of 300km. Plans to build these weapons — also known as Hrim-2 and equivalent to Russia’s Iskander — were announced as early as 2003. However Rochan Consulting, a military advisory, said such a missile should have been picked up by Russian air defence systems and said there was “no evidence to suggest that Russian air defence [nearby] was activated”.

Another possibility is that the strike was carried out by resistance fighters or Ukrainian special forces using kamikaze drones. A modified drone carrying explosives was used to attack the Black Sea fleet headquarters in Sevastopol in late July.

“It’s absolutely possible that it was a group of local saboteurs,” the European intelligence official said.

The mystery behind the explosions plays into Ukraine’s hands, emphasised the Nato official. “Why take credit when you can leave behind paranoia?” he said. “It’s not like the Russians don’t know what hit them.”

For Russia, blaming the attack on Ukraine would imply acknowledging weaknesses in its own defence and demand an immediate response because Putin considers the Crimean peninsula part of Russia.

“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,” said the Institute for the Study of War.

Crimea’s Russian-appointed governor Sergei Aksyonov responded to the Saki air base explosions by declaring a state of high terror alert across the peninsula, while insisting the situation was “under full control”.

In his daily address on the same day, Ukrainian president Volodymyr Zelenskyy did not explicitly refer to the explosions, but he had special words for the peninsula.

“Crimea is Ukrainian,” he said, “and we’ll never give it up.”

Additional reporting by Max Seddon in Riga

What does winning the war in Ukraine look like for Moscow and Kyiv? Our Moscow correspondent Polina Ivanova and Moscow bureau chief Max Seddon discussed in an Instagram live the future of the war. Watch it here.