(AFP) - The United States warned Monday it would take action against companies and nations working with Iran's drone program after Russia used the imports for deadly kamikaze strikes in Kyiv.

"Anyone doing business with Iran that could have any link to UAVs or ballistic missile developments or the flow of arms from Iran to Russia should be very careful and do their due diligence -- the US will not hesitate to use sanctions or take actions against perpetrators," State Department spokesman Vedant Patel told reporters.

"Russia deepening an alliance with Iran is something the whole world -- especially those in the region and across the world, frankly -- should be seeing as a profound threat," he said.

Patel said that the United States also believed that Iran's shipment of the drones -- formally known as unmanned aerial vehicles -- violated UN Security Council Resolution 2231, which blessed a now moribund 2015 nuclear deal.

"It is our belief that these UAVs that were transferred from Iran to Russia and used by Russia in Ukraine are among the weapons that would remain embargoed under 2231," he said.

The resolution's ban on Iranian exports of conventional weapons expired in October 2020 despite efforts at the United Nations by the administration of Donald Trump, who left the unclear deal.

But the resolution maintains restrictions through October 2023 on exports related to ballistic missiles that could deliver nuclear weapons.

Citing previously released US intelligence, Patel said that some of Iran's drones being sold to Russia have malfunctioned.

The transfer shows the "enormous pressure" on Russia, which according to US figures has lost 6,000 pieces of equipment since invading Ukraine, he said.

Moscow is "being forced frankly to resort to unreliable countries like Iran for supplies and equipment," he said.

US officials have previously said that Russia, historically a major arms exporter, is also turning to North Korea but that China has rebuffed calls for assistance.

© Agence France-Presse