This was reported by the UN Human Rights Monitoring Mission in Ukraine.
"One of the videos shows a brutal execution of a man who appears to be a Ukrainian prisoner of war, while the other one shows mutilated bodies of apparent Ukrainian servicepersons. Regrettably this is not an isolated incident," the statement said.
It is reported that these and other violations must be investigated and the perpetrators brought to justice.
"In recent reports the Mission documented a number of serious violations of International humanitarian law, including those committed against prisoners of war," the United Nations added.
Council of Europe Secretary General Marija Pejčinović-Burić also condemned the executions of Ukrainian soldiers by Russians.
"Horrified by the video circulating online showing Russian troops decapitating Ukrainian prisoner of war. This is inhuman and I condemn it in the strongest possible terms. Those responsible must be held accountable," Marija Pejčinović Burić wrote.
On the evening of April 11, a video was posted online showing Russian occupiers executing a man, calling him a Ukrainian soldier. Ukrainian President Volodymyr Zelenskyy also reacted to the video.
Ukraine's Foreign Ministry is asking The Hague to respond to the video of the execution of a Ukrainian soldier by Russian soldiers. At the same time, Minister Dmytro Kuleba called for Russia's expulsion from the UN.
Putin's spokesman Dmitry Peskov commented on the video of the execution of a Ukrainian prisoner by the Russian military and said it needed to be verified.