Russia is running low on stocks of Iranian-made drones, according to the latest assessments by European officials.
They say use of the drones against Ukraine has fallen significantly over the past 10 days.
Previously, dozens of drones were regularly used against Ukrainian energy infrastructure, although most were shot down by the country’s air defences.
The Ukrainian government said in December that Russia had received an order of 250 drones from Iran, without saying where it got the information.
One source said Russia was constantly working to obtain more drones and other military supplies from Iran and other sources.
The supply squeeze comes as Russia’s war in Ukraine nears its one-year mark, and with fighting still bogged down in eastern areas, even as Moscow’s forces increase their attacks.
Russia has relied increasingly on drones and missiles to try to weaken critical infrastructure across Ukraine.
Drones and weapons supplied to Ukraine - in pictures
Ukraine’s allies have identified Tehran as a key supplier for Moscow’s war efforts.
Evidence shared among countries shows that drones seen in Ukraine have matching features with Iranian-made drones seen elsewhere, a source said.
Parts recovered in Ukraine, including engines and wing stabilisers, are also the same, the source said.
But Tehran has repeatedly denied shipping supplies of drones to Russia.
The lull could be due to the fact Russia is saving stocks for future attacks.
Russia and Ukraine conflict latest - in pictures
The G7 and the EU have been looking to disrupt the supplies, particularly focusing on companies in other countries and Russia’s access to any western components that could be used for military purposes.
The EU is discussing sanctions and export restrictions on seven Iranian entities this week, including those linked to Iran’s Islamic Revolutionary Guard Corps, as it tried to stop evasion of its sanctions.
“We propose, among other things, export restrictions on multiple electronic components used in Russian armed systems, such as drones, missiles, helicopters,” European Commission President Ursula von der Leyen said last week.
