The European Union on September 9 described as "credible" information provided by allies suggesting Iran has supplied short-range ballistic missiles to Russia to help Moscow wage war in Ukraine and hinted at a "swift" response.
The statement came after the Kremlin declined to directly refute the accusation and instead highlighted its cooperation with Tehran in "the most sensitive areas" while Iran "strongly rejected" the allegation.
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"We are aware of the credible information provided by allies on the delivery of Iranian ballistic missiles to Russia," EU spokesman Peter Stano said. "We are looking further into it with our member states and, if confirmed, this delivery would represent a substantive material escalation in Iran's support for Russia's illegal war of aggression against Ukraine."
Stano added that "the EU leaders' unanimous position has always been clear. The European Union will respond swiftly and in coordination with international partners, including with new and significant restrictive measures against Iran."
Earlier the same day, Dmitry Peskov, the spokesman for Russian President Vladimir Putin, said the Russian side had "seen this report."
But he did not appear to refute it.
"It is not every time that this kind of information is true," Peskov said. "Iran is our important partner, we are developing our trade and economic relations, we are developing our cooperation and dialogue in all possible areas, including the most sensitive areas."
Later, the Iranian Foreign Ministry issued a flat denial. "We strongly reject the claims on Iran's role in exporting arms to one side of the war," ministry spokesman Nasser Kanani told a press conference.
State Department spokesman Vedant Patel said on September 9 that the United States was "incredibly alarmed by reports of the transfer of Iranian missiles to Russia."
Patel told reporters at a briefing that if the reports proved to be true, it would mean a "dramatic escalation of Iran's support of Russia's war of aggression in Ukraine." He also confirmed that the United States would deliver "significant consequences" to Iran if necessary.
Analysts had suggested as rumors of a possible transfer of the weapons circulated that it would provide a boost to Russia's war efforts as its 36-month-old full-scale invasion of Ukraine continues.
Russian forces have purportedly used North Korean ballistic missiles, but North Korean production capacity is thought to be relatively small.
Russian Security Council Secretary and until recently longtime Defense Minister Sergei Shoigu visited Tehran in early August, contributing to concerns.
Russia has used Iranian-designed attack drones since the early months of the invasion, although Tehran has denied its drones are being deployed there.