Group of Seven (G7) leaders called on third parties to stop providing Russia with material support, naming Iran in their joint statement published on March 15.
Iran has been cooperating with Russia on military supplies since the first year of Russia's all-out war in Ukraine in 2022, becoming Russia's key drone provider.
In February, Reuters reported that Iran had already sent 400 ballistic missiles to Russia. Ukrainian authorities have not confirmed this claim.
"We are extremely concerned about reports that Iran is considering transferring ballistic missiles and related technology to Russia after having supplied the Russian regime with UAVs (unmanned aerial vehicles), which are used in relentless attacks against the civilian population in Ukraine," the statement reads.
Iran's involvement would lead to additional destabilization in the region and represent "a substantive material escalation" in its support for Russia's war, G7 leaders said.
The officials warned that they are prepared to respond "swiftly," including with new "significant measures" against Iran if it proceeds with supplying Russia with ballistic missiles or related technology.
The U.S. said in February it would impose new sanctions and "prepared to go further" if Iran sold Moscow ballistic missiles.
While Russia's use of Iranian missiles to attack Ukraine has not been confirmed, Ukrainian authorities have recorded several cases of North Korean missile launches by Russian troops.
One of the first cases was recorded on Dec. 30, 2023, during an attack on Zaporizhzhia, the Security Service of Ukraine (SBU) wrote. Later on, Russia also struck Kyiv and Kharkiv Oblast with North Korean weaponry.