Ukrainian President, Volodymyr Zelenskiy, accused Tehran of lying, saying Kyiv's forces were downing at least 10 of the unmanned aerial vehicles every day.
Iran has admitted that it sent drones to Russia, but insisted they were supplied before the Russian invasion of Ukraine.
Iran acknowledged for the first time on Saturday.
Iranian Foreign Minister Hossein Amirabdollahian said a "small number" of drones had been shipped a few months before Russia’s February 24 invasion, Reuters reports.
Ukrainian President, Volodymyr Zelenskiy, accused Tehran of lying, saying Kyiv's forces were downing at least 10 of the unmanned aerial vehicles every day.
In Iran's most detailed response to date, Amirabdollahian denied Tehran was continuing to supply drones to Moscow.
"This fuss made by some Western countries that Iran has provided missiles and drones to Russia to help the war in Ukraine - the missile part is completely wrong," the official IRNA news agency quoted him as saying.
"The drone part is true and we provided Russia a small number of drones months before the Ukraine war," he said.
This comes as tensions with the West escalated over protests in the country, Iranian aid to Russian war effort in Ukraine, and fears over Iran's nuclear programme.
Ukraine on Saturday warned Iran that "the consequences of complicity" with Moscow would be "greater than the benefit" of Russian support after Tehran admitted for the first time sending drones to Russia.
"Tehran should realise that the consequences of complicity in the crimes of the Russian Federation's aggression against Ukraine will be much greater than the benefit of Russia's support," foreign ministry spokesman Oleg Nikolenko wrote on Facebook.
Ukraine's state electricity operator on Saturday announced blackouts in Kyiv and seven other regions of the country in the aftermath of Russia's devastating strikes on energy infrastructure.
The move comes as Russian forces continue to pound Ukrainian cities and villages with missiles and drones, inflicting damage on power plants, water supplies and other civilian targets, in a grinding war that is nearing its nine-month mark.
A judge in a Ukrainian town controlled by Moscow was in a "serious" condition after surviving an assassination attempt, a Russia-backed separatist leader in Donetsk said Saturday.
"There was attempt with the use of firearms on a judge of the Supreme Court of the Donetsk Republic Alexander Nikulin," the rebel leader of the self-proclaimed republic, Denis Pushilin, said on Telegram.