Volodymyr Zelenskiy has fired the head of Ukraine’s air force a day after it emerged that a recently delivered F-16 jet had crashed earlier this week, killing the pilot.

“I have decided to replace the commander of the air forces … I am eternally grateful to all our military pilots,” Zelenskiy said in his evening video address on Friday, without giving a reason for the dismissal of Mykola Oleshchuk.

The crash was more unwelcome news in a week when Russia has continued to make rapid advances in eastern Ukraine toward the key city of Pokrovsk, sparking public criticism of the Ukrainian military leadership and Zelenskiy even as the bold incursion into the Russian Kursk region continues.

For months, Russian forces have been attempting to seize Pokrovsk, a strategically important mining town with a prewar population of about 60,000, but their advance has gained considerable momentum in recent weeks.