Iran plans to supply Russia with potentially hundreds of drones for its war in Ukraine, some with combat capabilities, a US official has said.
White House National Security Adviser Jake Sullivan said that information received by the US suggested Iran was preparing to train Russian forces to use the drones.
Drones have played an integral part in the war for both Ukraine and Russia.
Just last week, Ukraine appealed for donations of thousands of drones to aid its war efforts.
Both sides are using them to spot the enemy's positions and then help direct and correct their own artillery fire on a target.
The Kremlin has said Russian President Vladimir Putin will travel to Iran's capital, Tehran, on 19 July. He is expected to meet Iranian President Ebrahim Raisi and Turkey's Recep Tayyip Erdogan for peace talks on Syria.
Mr Sullivan added that intelligence received by the US supported the view that Russia's assault on eastern Ukraine was "coming at a cost to the sustainment of its own weapons".
His comments came ahead of US President Joe Biden's visit to Israel and Saudi Arabia this week. Neither country has so far joined sanctions against Russia over its war in Ukraine.
Israel sees Iran, which calls for its elimination, as its biggest regional threat.
The US and other allies have supplied billions of dollars' worth of weapons to Ukraine since the invasion in February.
Mr Sullivan said the US would continue to "sustain the effective defence of Ukraine".