Explosions at a Russian air base in Crimea could escalate or prolong the war in Ukraine. Here's everything you need to know:
What happened in Crimea?
A series of explosions rocked a Russian air base on the Crimean peninsula on Tuesday, killing at least one civilian and injuring 13 people, including two children, Russia claimed. Bystanders reported around 12 blasts.
According to The Washington Post, the Saki Air Base, which has been used to launch missile strikes against Ukraine, was located "in a coastal area presumed by the Russians to be so safe that videos showed startled beachgoers at a nearby resort scrambling for cover." Ukraine's air force reported that nine Russian military aircraft were destroyed.
Local authorities responded by raising the base's alert level as an "exclusively prophylactic" measure, Russian-installed Crimean leader Sergei Aksyonov said. Aksyonov also said very few people were evacuated following the explosions, but the U.S.-based Institute for the Study of War contradicted his claim, reporting that "social media footage showed long traffic jams ... and the departure of several minibusses, reportedly with evacuees."
Explosions were also reported at a Russian ammunition depot near Novooleksiivka, deep behind Russian lines in southern Ukraine, but information about the blasts remains scarce.
Who was behind the Crimea explosions?
According to Russia, no one. Officials blamed a potential "violation of safety requirements" for the detonation of what they said was air force ordnance stored on the base. Ukraine denied responsibility, with the country's Defense Ministry quipping on Facebook that the explosions reveal the importance of "fire safety and the prohibition of smoking in unspecified places."
On Wednesday, a Ukrainian government official broke with the official narrative, telling The Washington Post that Ukrainian special forces were responsible for the attack. In recent months, irregular Ukrainian partisan forces have pulled off a number of operations, including bombings and assassinations, in Russian-held Ukrainian territory. This admission, however, suggests "an increasingly important role for covert forces operating deep behind enemy lines as the country expands efforts to expel Russian troops," the Post reported.
It's unlikely that Ukraine could have carried out the attack without help from covert assets behind Russian lines. 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 New York Times reported. The ISW points out that Ukraine does not have long-range army tactical missile systems (ATACMS) but that the country's military "could have modified its Neptune [anti-ship] missiles for land-attack use."
The Saki Air Base is located about 100 miles from Crimea's border with Kherson Oblast and about 150 miles from the nearest Ukrainian-controlled territory.
What did Zelensky say?
Ukrainian President Volodymyr Zelensky did not mention the attack on Crimea in his daily video address, but he did say that it was fitting for Ukrainians to focus on Crimea. "Crimea is Ukrainian and we will never give it up," he said. "We will not forget that the Russian war against Ukraine began with the occupation of Crimea."
Russia annexed Crimea in 2014 after protests in Ukraine forced pro-Russian President Viktor Yanukovych from office. In less than three weeks, Russian troops entered Crimea, installed a friendly government, and held a referendum — dismissed by most of the international community as fraudulent — in which Crimeans voted overwhelmingly to join with Russia. Occupying Russian forces are expected to hold similar referenda in the Donbas and southern Ukraine as early as next month.
Despite Zelensky's insistence on total victory, retaking Crimea would be very difficult to achieve. First, Ukrainian forces would have to liberate vast swaths of Russian-held territory in southern Ukraine. Then, they would need to launch an offensive larger than any they've attempted since the war began. And finally, an attack on Crimea would risk massive retaliation. The Kremlin would consider an attack on Crimea to be an invasion of Russia, a move former Russian President Dmitry Medvedev said would trigger "Judgment Day."
If Zelensky insists on continuing to fight until Crimea is back in Ukrainian hands, the war could either stretch on for years — or end in blood and fire on a scale not seen since the Second World War.
Has Ukraine struck behind Russian lines before?
Maybe. On April 1, Russian Gov. Vyacheslav Gladkov blamed explosions at a fuel depot in Belgorod, Russia, on "an airstrike coming from two helicopters of the Ukrainian armed forces." Several other incidents followed, damaging or destroying storage depots, a chemical plant, and a defense research site inside Russia.
Ukraine never claimed responsibility for any of the attacks, but Ukrainian presidential adviser Mykhailo Podolyak did suggest on Twitter that the explosions could be "karma for the murder of [Ukrainian] children." Analysts have suggested that the true cause could involve either sabotage or Russian negligence.
BBC Monitoring's Vitaliy Shevchenko wrote in April that neither side would benefit if it came to be widely known or believed that Ukraine was behind the attacks. "Ukrainian attacks on Russian territory would be an embarrassment to the Kremlin" as well as "a major escalation" for Ukraine.