In a letter to the United Nations on Friday, France, Britain and Germany called for an “impartial” investigation into Iranian drones, which the West says Russia is using in the war in Ukraine.

“We would welcome an investigation by the UN Secretariat team responsible for overseeing the implementation of UNSCR 2231,” the UN ambassadors of the three countries wrote.

UN Security Council Resolution 2231 approved the international deal, which provided for sanctions relief in exchange for restrictions on Iran’s nuclear program – a deal later scrapped by then-US President Donald Trump.

In their letter, addressed to the Security Council and Secretary-General Antonio Guterres, the ambassadors said they would “stand ready to assist the Secretariat’s work in conducting its technical and impartial investigation.”

They added that they were “deeply concerned about the transfer of unmanned aerial vehicles (UAVs) from Iran to Russia in violation” of the resolution.

“These UAVs are used by Russia in its war of aggression against Ukraine in attacks on civilian infrastructure and cities across Ukraine, resulting in the deaths of innocent civilians,” they wrote.

French UN ambassador Nicolas de Riviere called on Iran to “immediately end any form of support for Russian aggression against Ukraine”.

Western countries have accused Iran of supplying drones that Moscow uses for strikes in Ukraine, and the White House said Thursday that Iranian personnel are on the ground in Crimea to help Russian forces conduct drone strikes.

However, Russia’s UN envoy Vassily Nebenzia called the indictment “another falsification (news) about the alleged shipments to Russia… We reject all attempts to involve the UN Secretariat in this dirty enterprise.”

Iran also firmly denied drone allegations at the United Nations earlier this week.