Ukraine's air defense capability to intercept Russian missiles and drones is expected to decline unless it gets additional weapons supplies from Western nations.
Ukrainian President Volodymyr Zelenskyy has repeatedly asked Western leaders for new military assistance to improve his country's air defenses.
However, the United States, the largest supporter of Ukraine, has yet to send new aid to Kyiv due to a stalemate in Congress over an emergency budget bill that includes aid to Ukraine.
The New York Times said on Friday that US government officials had assessed that Ukraine had only enough air defenses to last until next month unless they get resupplied.
A US think tank, the Institute for the Study of War, said on Saturday that the "intensification of the Russian strike campaign in recent weeks likely further pressured Ukraine's air defense umbrella."
The institute warned that if the Russian military conducts consistent large-scale aviation operations supporting Russian ground offensives in Ukraine, that would represent a ''significant threat'' to Ukraine.
Zelenskyy on Sunday appointed former first deputy defense minister, Oleksandr Pavliuk, as the new commander of Ukraine's ground forces.
Pavliuk replaces Oleksandr Syrskyi who was promoted to commander-in-chief of the armed forces in a bid to bring a new approach to Ukraine's counteroffensive.