The Azov Sea lies between Russia and Ukraine. Moscow controls its entire coast after seizing large swathes of southeastern Ukraine during its invasion and the 2014 annexation of Crimea.

Kyiv initially said it had downed both an A-50 Russian reconnaissance plane and a Il-22 bomber, but later said the latter made it back to base seriously damaged.

Ukraine's commander-in-chief, Valery Zaluzhny, said both planes were "destroyed", adding: "I am grateful to the air force for the excellently planned and conducted operation in Azov region!"

Ukrainian air force spokesman Yuriy Ignat later said the Ilyushin bomber made it back to the southern Russian city of Anapa, but claimed it was damaged beyond repair.

"The plane caught fire, there are wounded among the crew," he said, in a statement that AFP was not able to verify.

The A-50 is a Russian reconnaissance plane, equivalent to the AWACS (Airborne warning and control system) plane, used by NATO.

Moscow did not comment on the claims.

Kremlin spokesman Dmitry Peskov told reporters he had "no information" and that further questions should be directed to the defence ministry.

But Russian military bloggers with close army links did report an incident over the Azov Sea.

Telegram channel WarGonzo acknowledged that the A-50 was downed.

"Unfortunately war is never without tragedies, and the death of our fighters always hurts. We express our condolences to the families and close ones of the crew," it said.

It too reported that the Il-22 was able to make it back to base.

"According to reports, the pilots were able to land the damaged machine," it said.

"There is a fallen A-50, and a saved Il-22," another influential military blogger, Alexander Kots, said on Telegram, hailing the bomber jet's crew for landing the damaged plane "heroically."

The war in Ukraine has seen an escalation in attacks in recent weeks.