A blast on Thursday killed a police officer in the Moscow-controlled Ukrainian city of Melitopol, Russian authorities said, in the latest in a series of such attacks.
Melitopol, with a pre-war population of around 150,000 people, was captured early after Russia invaded Ukraine in February last year and now lies some 65 kilometers (40 miles) behind the frontline further north.
"Today at about 5:15 a.m. (02:00 GMT) there was an explosion at the entrance of an apartment building in Melitopol," the local branch of the Russian Interior Ministry said.
"Two policemen were injured and hospitalized. Subsequently, one of them died," it added.
It published a video showing a crater next to the entrance of a building block and several nearby cars with shattered windows.
The Ukrainian mayor of the city Ivan Fedorov, who is working from territory controlled by Kyiv, said the dead policeman was Oleksandr Mishchenko who had "not only defected to the side of the enemy, but also tricked his employees into becoming traitors."
"The path of each collaborator is predictable: yesterday betrayal, today panic, tomorrow massacre," he said.
Melitopol is in Zaporizhzhia, one of four regions — along with Donetsk, Luhansk, and Kherson — that Russia claimed to have annexed last year despite not having full military control over them.
Last year several Russian-linked officials were killed in attacks in territories controlled by Moscow's forces.
In December a car explosion killed an official in the village of Lyubimivka in occupied southern Ukraine.
The deputy head of the Russian-installed administration in Berdyansk, and his wife Lyudmyla who headed the electoral commission were killed in September.
That same month, the Luhansk separatist administration's top prosecutor and his deputy were also killed in an attack.