The suspect, Sergei Denysenko, will be held in custody pending trial, a spokesman for the court in the southwestern city of Krasnodar told Russian state-run agency TASS.

Denysenko admitted to the killing of recruitment official Stanislav Rzhitski, according to TASS, but denied working for Ukrainian secret services, instead insisting his motives were personal.

Denysenko was detained on Tuesday at an apartment in the town of Tuapse to the south of Krasnodar, where he was found in possession of a pistol.

Rzhitski, a deputy to the Krasnodar city administration official in charge of "mobilisation operations" for the army, was found dead in the city on Monday.

The 42-year-old, who previously served as a submarine commander, was shot while out for a jog according to Russian media.

Since April, the Russian army has been conducting a vast military recruitment operation, running massive advertising campaigns, promising big salaries and other perks.

The aim of the drive is to replenish forces on the frontline in Ukraine, without resorting to another mobilisation -- a step that the Kremlin took last September which proved unpopular.

In a sign of a degree of hostility towards the conflict, dozens of people have been arrested and accused of setting fire to -- or planning to set fire to -- recruitment centres since the beginning of the offensive in Ukraine.