Ukrainian President Volodymyr Zelenskyy said Russian army has suffered its biggest losses in decades and claimed that 31 Russian battalion tactical groups have been rendered incapable of combat, Reuters reported. 

Zelenskyy made the remarks on a televised address on Saturday. 

He also demanded the release of the mayor of Melitopol, who was allegedly kidnapped by Russian forces. 

The president said that Ukrainian forces were fully upholding the Mariupol corridor ceasefire and called for Russia to do the same.