Foreign Minister Hossein Amirabdollahian told state-linked media that Tehran was “against arming both Russia and Ukraine”.
“We have not supplied Russia with any weapons or drones for use in the war against Ukraine,” he said on Monday.
He did not clarify what action Tehran would take in the event of a definitive UN conclusion on the source of the drones.
Mr Amirabdollahian also reaffirmed his country's willingness to hold direct talks with Ukraine on the matter, and said that he conveyed this to European foreign policy chief Josep Borrell in the past days.
“I stressed to Mr Borrell that if … it becomes clear to us that Russia has used Iranian drones in the war against Ukraine, we will definitely not be indifferent about this issue.”
His remarks come after a warning by US House Speaker Nancy Pelosi that Iran was making a “big mistake” in supplying weapons to Russia.
Kyiv and its western allies have repeatedly accused Moscow of using Iranian-made drones in attacks on Ukraine in recent weeks.
Both the EU and US said they had ample evidence to support Ukraine’s assertion that Iranian drones have been found in the country.
Iran has rejected the allegations in the past while the Kremlin said western countries aimed to put pressure on Tehran.
According to analysts, Russia has launched dozens of drone attacks in Ukraine using Iran-made Shahed-136 “loitering munitions,” also called “kamikaze drones”, destroying power stations and other civilian infrastructure.
Russia has renamed the Shahed-136 the Geran-2.
Another type of Iran-made drone, the Mohajer-6, has also been found in Ukraine, completely intact after it crash-landed near Ukrainian defences.
The US issued a warning in June that Russia was set to receive “hundreds” of the low-cost weapons, which have been used by Iran’s allies in the Middle East to attack Saudi Arabia, the UAE, coalition forces in Iraq and targets inside Yemen.
The drones have often been used against civilian infrastructure.
Iran has been hit with new US and EU sanctions, which analysts said had probably derailed or at least frozen an effort to return to a deal on its nuclear programme, a move that would have resulted in sanctions being lifted in exchange for UN inspections of the country's nuclear facilities.
Earlier on Monday, Iran's foreign ministry spokesman Nasser Kanani rejected US allegations that Iranian military personnel were on the ground in Russian-occupied Crimea to help Moscow carry out drone attacks in Ukraine.
“We strongly reject this news,” Mr Kanani said at a press conference.
The claim by Washington “aims to deviate public opinion from the destructive role they have in the Ukraine war by standing on one side of the conflict and heavily exporting weapons and equipment to Ukraine”, he said.
His remarks were in response to White House national security spokesman John Kirby, who said last Thursday that Iranian forces were “on the ground in Crimea” to assist Russia in its operations, and the personnel were trainers and technology support workers.
“Tehran is now directly engaged on the ground, and through the provision of weapons that are impacting civilians and civilian infrastructure in Ukraine,” Mr Kirby said.
The US, Britain and the EU have already imposed sanctions on Iran over the issue of the drones.
Last month, Kyiv decided to significantly reduce its diplomatic relations with Tehran over the alleged arms deliveries to Moscow.