The Biden administration warned Thursday of a "swift and severe response" from the international community if Iran proceeds with potential transfers of ballistic missiles to Russia.
The exhortation came one day after Reuters reported that Tehran had already supplied Moscow with 400 Fateh-110 missiles.
Three anonymous Iranian officials told the news agency that additional deliveries are expected in the coming weeks. Previous shipments have been sent by plane and ship across the Caspian Sea, which borders northern Iran and southern Russia.
National Security Council spokesperson John Kirby said Washington has been "monitoring" the issue closely, but no evidence has emerged that missiles have been shipped from Iran to Russia.
Still, he acknowledged that the Biden administration has "no reason to believe that they will not follow through."
"If Iran proceeds with this provision of ballistic missiles, I can assure you that the response from the international community will be swift and it will be severe," he told reporters during a virtual briefing.
That will include Washington taking the matter up within the UN Security Council and imposing additional sanctions on Iran.
Those penalties would come in addition to sanctions that are expected to be announced later this week on Iran in retaliation for its ongoing aid to Moscow for its war on Ukraine, including the provision of lethal drones, guided aerial bombs and artillery rounds.
"We are prepared to go further if Iran sells ballistic missiles to Russia," said Kirby.
It is unclear when the sanctions that have been finalized will be announced, but the US is slated to announce penalties on Russia on Friday for its war on Ukraine, and the death of Russian opposition leader Alexey Navalny, who died in a prison last week.
US President Joe Biden warned of "devastating" consequences if Navalny died following a 2021 summit with Russian President Vladimir Putin.
