Ukrainian forensic experts have so far exhumed 146 bodies, mostly civilians, at a mass burial site near the town of Izium in eastern Ukraine and some bear signs of a violent death, the regional governor said on Monday.

President Volodymyr Zelenskyy has said some 450 bodies are believed to have been buried at the site in a forest on the outskirts of Izium, which was recently recaptured by Ukrainian forces during a counteroffensive in the Kharkiv region.

Oleh Synehubov, governor of the Kharkiv region, said the exhumed bodies included two children.

"Some of the dead have signs of a violent death. There are bodies with tied hands and traces of torture. The deceased were also found to have explosive, shrapnel and stab wounds," Synehubov wrote on the Telegram messaging app.

The forensic experts, dressed in white protective suits and wearing rubber gloves, have been working methodically for days to exhume and identify the bodies, whose makeshift graves were marked by flimsy wooden crosses.

Kremlin spokesperson Dmitry Peskov on Monday rejected Ukraine's allegations as a "lie."

Residents have previously said some of the graves in the forest were of people who died in a Russian airstrike.