Russia and Ukraine are increasingly facing a need for air defense systems to fend off drone attacks.

The Russian defense ministry on Monday said its air defenses destroyed a Ukrainian drone over the Smolensk region, west of Moscow.

The ministry said Ukraine launched such strikes in five regions, including Moscow, between Saturday evening and Sunday's pre-dawn hours.

Ukrainian intelligence is believed to have staged the drone assaults in retaliation after Russia used unmanned aerial vehicles in unprecedented-scale attacks on Kyiv and other regions.

Britain's defense ministry on Sunday said Russia probably moved strategic air defense systems from its Baltic coast enclave of Kaliningrad to the Ukraine front.

Kaliningrad is a strategic hub close to NATO member countries, including three Baltic states.

The British intelligence update said the move follows an uptick in losses of Russia's state-of-the-art S-400 air defense systems to Ukraine. It notes the move "highlights the overstretch the war has caused for some of Russia's key, modern capabilities."

The development comes as Ukraine is calling on the West for assistance to boost its air defense.