Ukraine said on Friday it would downgrade diplomatic ties with Iran and strip the ambassador of his accreditation over what it called Tehran's "unfriendly" decision to supply Russian forces with drones.

Earlier in the day, Ukraine said it had downed four Iranian-made "kamikaze" unmanned aerial vehicles, prompting President Volodymyr Zelenskiy to complain Tehran was harming Ukrainian sovereignty and its citizens.

Ukraine and the United States have accused Iran of supplying drones to Russia, something Tehran has denied.

"Supplying Russia with weapons to wage war against Ukraine is an unfriendly act that deals a serious blow to relations between Ukraine and Iran," said a statement on the foreign ministry's website.

"In response to such an unfriendly act the Ukrainian side has decided to deprive the ambassador of Iran of his accreditation and also to significantly reduce the number of diplomatic staff of the Iranian embassy in Kyiv."

The message was handed to the acting ambassador since the permanent envoy, Manouchehr Moradi, is not currently in Ukraine.

Military authorities in southern Ukraine said in a statement they had shot down the Shahed-136 unmanned aerial vehicles over the sea near the port of Odesa.

Military experts say the drones would be useful to Russia for both reconnaissance and as loitering munitions that can bide their time in locating and engaging suitable targets.