Russian forces announced today they had abandoned the strategic Black Sea outpost of Snake Island, in a major victory for Ukraine that could loosen the grip of Russia's grain export blockade.

Russia's defence ministry described the decision to withdraw from the outcrop as a "gesture of goodwill" that showed Moscow was not obstructing United Nations efforts to open a humanitarian corridor allowing grains to be shipped from Ukraine's ports.

But Ukraine said it had driven the Russian forces out after massive artillery and assault overnight.

"Kaboom!" tweeted Andriy Yermak, Ukrainian President Volodymyr Zelenskiy's chief of staff. "No Russian troops on the Snake Island anymore. Our armed forces did a great job."

Ukraine's southern military command posted an image on Facebook of what appeared to be the island, seen from the air, with five huge columns of black smoke rising above it from what it described as an assault by missiles and artillery.

"The enemy hurriedly evacuated the remains of the garrison with two speed boats and probably left the island. Currently, Snake Island is consumed by fire, explosions are bursting."

Reuters could not immediately verify the photograph of either side's battlefield accounts.

The outcrop controls access to sea lanes to Odesa, Ukraine's main Black Sea port, where a Russian blockade has prevented exports of grain from one of the world's main suppliers, creating a global food supply shock and risk of famine.

Russia captured it on the war's first day, when a Ukrainian guard there, ordered to surrender, radioed back "Russian warship: go fuck yourself."

The incident was immortalised on a Ukrainian postage stamp. The day the stamp was issued, Ukraine sank the ship, the flagship of Russia's Black Sea fleet.

- Reuters