The White House said on Tuesday it was concerned that Iran might be providing Russia with ballistic missiles for use in its war against Ukraine.
Moscow is already receiving Iran’s help with Shahed drones, guided aerial bombs, and artillery ammunition and may be gearing up “to go a step further in its support for Russia”, said National Security Council spokesperson John Kirby.
Moscow has received hundreds of Shahed drones that the Russian military used against Ukraine’s energy facilities and other key infrastructure.
"We are therefore concerned that Iran is considering providing Russia with ballistic missiles now for use in Ukraine," Mr Kirby told reporters.
Vladimir Putin, in return, is offering Tehran “unprecedented defence cooperation, including on missiles, electronics and air defence", he said.
The White House official cited a September meeting when Iran hosted Russian defence minister Sergei Shoigu to show off a range of ballistic missile systems.
Mr Putin’s war in Ukraine has also led Moscow to deepen ties with Iran. Iran also has reportedly shared its drone technology with Russia, which built a facility to produce them. In return, Moscow is expected to offer Iran advanced -35 fighter jets and other modern weapons.
Mr Kirby said Iran was looking to buy additional military equipment from Russia, including attack helicopters, radars and combat-trainer aircraft.
"In total, Iran is seeking billions of dollars worth of military equipment from Russia to strengthen its military capabilities," the NSC official said.
"Russia has also been helping Iran develop and maintain its satellite collection capabilities and other space-based programmes."
The burgeoning military partnership between Iran and Russia is harmful to Ukraine, Iran‘s neighbors in the Middle East and "quite frankly to the international community," he said.
The warning from White House comes at a time when Joe Biden is pushing for more than $61bn in emergency US funding to continue to support Ukraine’s defence, which has remained stalled in the Congress. The additional aid for Ukraine is part of a larger $106bn funding request from the Democratic president that also would support Israel, Taiwan and the US operations on the border with Mexico.
The Russian president has shown desperation by increasing reliance on Iran, as well as North Korea, the two nations largely rejected on the international stage for their nuclear programs and human rights records, according to the US.
This will help Russia restock its ammunition reserves as it is facing depletion of its stock in a lengthy invasion of Ukraine, which it had anticipated to be a shorter operation.
The White House has said Russia has turned to North Korea for artillery.