Ukrainian leaders are bracing for major missile attacks as the first anniversary of Russia's invasion approaches on Friday.

President Volodymyr Zelenskyy said in a video message on Sunday that the more losses Russia suffers in the eastern region of Donbas, the faster Ukraine will be able to end the invasion.

Zelenskyy explained that military commanders who have been briefing him from the frontline said "the situation is very difficult" near the town of Vuhledar in the eastern region of Donetsk.

But he added, "We are breaking the invaders and inflicting extremely tangible losses on Russia."

Ukraine's presidential adviser Mykhailo Podolyak said on Saturday that he expects Russia to launch missiles against his country from Tuesday to Friday.

Ukraine's National Security and Defense Council Secretary Oleksiy Danilov also said Russia is preparing massive missile attacks on Thursday and Friday.

Russian President Vladimir Putin is expected to deliver his state of the nation address on Tuesday.