A Russian military officer who had defected from Ukraine was killed in a bomb blast on Thursday in Russia-annexed Crimea in a targeted assassination plot, the regional governor said.

Robert Shageyev was a former Ukrainian naval officer who fled to Crimea after switching allegiance to Russia during Moscow’s annexation of Crimea in 2014, according to Russian Telegram channels.

He was commanding Ukraine’s only submarine, the Zaporizhzhia.

Russia's Federal Security Service confirmed the death of a military official and announced the detention of a woman, a Russian national, suspected of carrying out the attack.

The suspect was acting “on instructions from Ukrainian intelligence agencies,” said Sevastopol’s governor Mikhail Razvozhayev on Telegram.

The regional governor did not identify the victim or the suspect.

The attack took place in Sevastopol, the biggest city in Russian-annexed Crimea, when the man was walking down a staircase with a friend, said the state-run TV channel Russia 24, citing the country’s Federal Security Service.

The explosive device had been planted inside a bin near a bench, it reported. The man died instantly on the spot.

The explosion was accompanied by a loud bang, eyewitnesses were quoted as saying. Witnesses also claimed to have seen a woman standing with a backpack in the same area.

Myrotvorets, an unofficial Ukrainian website that keeps a database of people described as war criminals or traitors, said Shageyev had been “liquidated”.

Ukraine has not publicly commented on the attack.

This is not the first time Russia has blamed Ukraine for the assassination of a senior military official. Moscow has blamed Kyiv for a string of attacks on important figures, particularly those linked to Moscow's war effort, on Russian soil.

Ukrainian sources have claimed responsibility in some cases, while denying others.

Shageyev joined Russia’s Black Sea Fleet after he surrendered the Ukrainian submarine to Russian forces with little resistance. He subsequently swore allegiance to the Russian military, according to local media reports.

In 2014, a Ukrainian defence ministry spokesperson said the submarine Zaporizhzhia had been taken over and placed under the flag of the Russian naval fleet after its commander abandoned it.

Ukrainian authorities notified Shageyev as the subject of a suspected treason case in July 2022.

After switching sides, he was reported to have been appointed as commander of a submarine division in Sevastopol Bay in 2015. He then commanded the Russian submarine B-262 Stary Oskol from 2017 to 2018.

Separately, Mr Razvozhayev said five people were killed in Sevastopol overnight during an operation to dispose of an explosive device.