The UK defense ministry says that there have been no reports of Iranian-made attack drones being used in Ukraine since around February 15.
The ministry said in its intelligence update on Saturday that the lack of such deployment "likely indicates that Russia has run down its current stock."
It added that "Russia will likely seek a resupply."
Fighting in the eastern parts of Ukraine is raging as the aggression has now entered its second year.
The Russian defense ministry announced on Saturday that its forces had attacked Ukrainian troops and weapons depots in the eastern regions of Donetsk and Kharkiv.
The Ukrainian General Staff also announced that the Russian forces continue to shell Bakhmut and Lyman, two of the key cities in the Donetsk region.