According to government sources in Kiev, they are the remains of several civilians and servicemen

Ukraine: new mass grave with about 17 bodies in Kharkov

AP/OLEKSANDR RATUSHNIAK - Ukrainian servicemen walk past the fragments of a downed plane in Kiev, Ukraine, Friday, Feb. 25, 2022

Ukrainian authorities reported Thursday the discovery of a mass grave with at least 17 bodies near the village of Kopanki, in the Kharkov region (northeast), recently retaken by Ukrainian forces.
 
According to preliminary data provided today by the Interior Ministry, the burial site contains bodies of both civilians and soldiers.
 
"The locals informed the investigators that the occupation forces collected the bodies of the dead from the area. On 13 April, they brought two trucks, dug a three-metre deep hole and dumped the bodies in it," the Ministry explained in a statement.
 
Subsequently, the ground was levelled with tanks and the Russian soldiers did not allow the villagers to mark the site or leave any markings on the grave, the source said.
 
The Ukrainian government reported yesterday that a thousand bodies have already been exhumed from the territories recaptured in eastern Kharkiv and northern Donetsk as part of the ongoing counteroffensive against Russian forces.
 
The largest concentration of graves has so far been located in the vicinity of the town of Izium, where the remains of 447 people were recovered.