Moscow has made a string of arrests of people it says have sponsored the Ukrainian army since Russia launched its full-scale military campaign against its neighbour in February last year.

The FSB security agency said Thursday it had arrested a former civil servant in the southern Rostov region on suspicion of "treason" -- charges that carry up to 20 years in prison.

"Since May 2018, the former employee of a state body made more than 60 transfers totalling over 330,000 rubles ($3,700) to Ukrainian bank accounts used to finance the armed forces of Ukraine," the TASS news agency cited the FSB as saying in a statement.

It did not name the individual or say which government agency they worked for.

Investigators said the money was used to purchase weapons and uniforms for Ukrainian soldiers, including before February 2022, when Russian-backed separatist forces were fighting against the Ukrainian army in the eastern Donbas region.

Against the backdrop of its offensive on Ukraine, Moscow has escalated an intense domestic crackdown on dissent, handing out long prison sentences to those who speak out against the conflict or publicly back Ukraine.