Nine Russian warplanes were destroyed in explosions at a military base in Crimea on Tuesday, according to Ukraine's air force.
Two US newspapers reported that Ukrainian special forces had carried out an attack on the Russian-annexed peninsula.
But Ukrainian officials have not publicly claimed responsibility for the blasts, which Russia said may have been caused by a "careless smoker" causing munitions to catch fire and blow up.
President Volodymyr Zelenskyy last night said that Crimea was a fundamental strategic objective.
“This Russian war against Ukraine and against all of free Europe began with Crimea and must end with Crimea - its liberation,” Zelenskyy said.
Russia has denied any aircraft were damaged in the blasts in Crimea.
A Russian critic who burned his passport while protesting the war in Ukraine is facing possible extradition over "trumped-up" tax evasion charges.
Alexey Alchin, 46, who lives in Bulgaria, could be sent to Moscow to face allegations that he failed to pay VAT debts of over 282.5 million roubles (€4.5m) in late 2015.
Alchin claims to have settled his debts before leaving Russia and said he knew nothing of the charges which Moscow officials insist go as far back as 2018.
A court in Bulgaria has approved Russia's request for Alchin's extradition, sparking a backlash over the the decision.
Alchin's wife Olga Gyurova believes her husband is being persecuted by Moscow for his political leanings and anti-war stance.
In February, Alchin took part in an anti-war protest in Varna, Bulgaria, where he burned his Russian passport.
If the extradition is to go ahead, it would make Bulgaria the first European Union member state to hand over a Russian national since the country's invasion of Ukraine in February.
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