Several European Union foreign ministers have called for sanctions against Iran over the transfer of Iranian drones to Russia, as the bloc agreed a separate set of asset freezes and travel bans over Tehran's crackdown on protests.

Ukraine has reported a spate of Russian attacks with Iranian-made Shahed-136 drones in recent weeks, saying that Iran was responsible for the "murders of Ukrainians".

Iran denies supplying drones to Russia since its invasion of Ukraine. The Kremlin has not commented.

"I think it (new sanctions) should be worked out immediately," Estonian Foreign Minister Urmas Reinsalu said as EU foreign ministers were due to discuss the transfer of Iranian drones to Russia.

Police officers check the explosion site after a drone attack in Kyiv

Mr Reinsalu said Ukrainian reports on the Iranian origin of the drones should be taken seriously, with sanctions acting as a deterrent to show "this has consequences."

France and Germany, both parties to the 2015 nuclear deal with Iran, have also made it clear they believed new sanctions in connection to the drones were necessary and that the drone transfers should be seen as a violation of a UN Security Council resolution.

The EU could move towards imposing new sanctions against Iran over the matter, according to two diplomats involved in preparing talks among the ministers, though no detailed decisions are expected today.

"Iranian drones are used apparently to attack in the middle of Kyiv, this is an atrocity," Denmark's Foreign Minister Jeppe Kofod said as he arrived at the meeting of EU foreign ministers in Luxembourg, urging a response.

EU foreign policy chief Josep Borrell said the bloc would look for hard evidence about Iran's role.

The United States has also warned it would take action against companies and nations working with Iran's drone programme.

"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.

Mr 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.

"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.

Citing previously released US intelligence, Mr 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.

Russia 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.

Sanctions deepened over protest crackdown
Meanwhile, the EU foreign ministers added 11 Iranians and four institutions, including Iran's morality police chief, to a travel ban and asset freeze list for their role in the crackdown on protests after the death in custody of 22-year-old Mahsa Amini.

"Unanimous decision today to take action against those in Iran responsible for the death of Mahsa Amini and violent repression of peaceful protests," Mr Borrell tweeted.

Tehran says it is keeping order against foreign-instigated troublemakers.

Additional EU sanctions on Iran will not be limited to blacklisting some individuals should Tehran's involvement in Russia's war on Ukraine be proven, Luxembourg's Foreign Minister Jean Asselborn said.