(Bloomberg) -- Group of Seven nations warned Iran against providing ballistic missiles to Russia for the war in Ukraine, threatening a swift response if it does so.

A senior Biden administration official said Friday the US has no proof Iran has delivered the missiles to Russia, but said the nation and its allies are increasingly alarmed by reports suggesting Tehran has done so.  

“Were Iran to proceed with providing ballistic missiles or related technology to Russia, we are prepared to respond swiftly and in a coordinated manner including with new and significant measures against Iran,” the statement released Friday says.

The allies said they were “extremely concerned” with the possibility of a missile transfer by Iran, adding it would “add to regional destabilization and represent a substantive material escalation in its support for Russia’s war in Ukraine.”

One option under consideration is an effective ban on Iran Air flights into Europe, according to the senior Biden administration official, who briefed reporters ahead of the statement.

The warning comes in response to signals that Iran is seeking deeper military cooperation with Russia, including by supplying surface-to-surface missiles to Moscow. The senior administration official said the US and its allies are closely watching the situation and planning for the transfer to occur.

Fresh US military support for Kyiv remains stalled, putting the nation at a disadvantage as Russia’s campaign stretches into its third year.

President Joe Biden’s administration announced last month it would impose new sanctions on Iran for supporting Russia’s invasion, following a Reuters report the nation was preparing to transfer ballistic missiles to the Russian military. Iran is already heavily sanctioned by the US, so the measures amounted to a largely symbolic rebuke. 

The US has said Russia is increasingly looking to Iran and North Korea for weapons, an effort to work around sanctions intended to cripple Moscow’s war machine. North Korea has denied it is sending weapons to Russia.

Iran is already supplying Russia with drones, guided aerial bombs and artillery ammunition for its war against Ukraine, according to the official, who added giving ballistic missiles would mark an escalation by Tehran.

(Updates with additional quotes, details starting from second paragraph)

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