White House has alleged that Iran deployed military experts in Russian-occupied Crimea to help launch drone attacks on Ukraine.
The Iranians are trainers and tech support workers, a US spokesman said, reports BBC.
"We assess that Iranian military personnel were on the ground in Crimea and assisted Russia in these operations," said White House national security spokesman John Kirby.
A "relatively small" number of Iranians are providing technical support and Russians are piloting the drones in Ukraine, he alleged.
Kirby said, "Tehran is now directly engaged on the ground, and through the provision of weapons that are impacting civilians and civilian infrastructure in Ukraine."
Ukraine’s capital Kyiv was struck by so-called "kamikaze" drones on Monday, deployed by Russia but believed to be Iranian-made.
The UK has already announced sanctions on Iranian businesses and individuals responsible for supplying the drones.
Bd-pratidin English/Golam Rosul