WASHINGTON 

Iran's sale of military UAVs to Russia violates existing UN Security Council prohibitions, the State Department said on Monday as Ukraine confronted waves of suicide drone attacks from Russia. 

"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," spokesman Vedant Patel told reporters.

The State Department was referring to a 2015 Security Council resolution that endorsed the landmark nuclear accord Iran struck with world powers. It lifted many sanctions imposed on the Islamic Republic in return for Tehran agreeing to curb its nuclear activities and allowing an international inspections regime to take effect.

The resolution also established a 2020 deadline for an arms embargo to be lifted, and former President Donald Trump unsuccessfully lobbied to have it extended. It does, however, maintain restrictions on the transfer of certain military technologies through 2023.

France and the UK last week first suggested that Iran's sale of drones to Russia is in violation of the UN resolution.

Iran has repeatedly rejected claims from the West that it is supplying Iranian-made drones to Russia for use in Ukraine as Moscow ups the ante with a series of strikes on Ukrainian cities in recent weeks.

Multiple images posted on social media appear to show Iranian-made Shahed drones, which Russia refers to as Geran-2, in the skies above Kyiv, as well as debris from the aircraft after they struck their targets.

On Monday, multiple explosions were heard in Ukraine’s capital of Kyiv as authorities reported waves of attacks by Russian kamikaze drones.

Patel warned that 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," he said.