“Naturally Russia will itself search for those who committed this crime. They must be found and punished,” Russian presidential spokesman Dmitry Peskov told reporters.
He added that Moscow will turn to international bodies for this purpose, “if this can be useful”.
Russia on Friday accused Ukraine of executing more than ten of its soldiers who had laid down their arms, based on videos posted on social networks.
On the first video, a dozen soldiers presumed to be Russian come out one after the other from a shelter, hands in the air, and lie face down on the ground under the injunction of apparently Ukrainian soldiers who hold them at gunpoint.
The video abruptly ends when a last silhouette emerges from the shelter and seems to open fire. Another video filmed by a drone shows the same place with a dozen bodies of soldiers lying in pools of blood.
On Sunday, Ukrainian human rights official Dmytro Lubynets said the videos showed a “feigned surrender” and that Russian soldiers had “committed a war crime by opening fire on Ukrainian armed forces”.
The Russian soldiers killed in this incident “cannot therefore be considered as prisoners of war”, he argued.