Ukrainian officials said on Sunday that there is mounting evidence that an explosion at a Russian penal colony that killed dozens of Ukrainian prisoners was ordered and carried out by Russian forces, citing newly released satellite photos as evidence that the soldiers were not killed in a missile strike.
Since the explosion late Thursday at the camp in Russian-controlled territory in eastern Ukraine, both sides have traded accusations over what was the source of the blast that killed at least 50 prisoners, many considered national heroes after being captured during a siege of a steelworks in the coastal city of Mariupol.
While the Russian Ministry of Defense said on Sunday it would allow the International Committee for the Red Cross and the United Nations access to the blast site, neither organization confirmed the claim. The Red Cross said in a statement Saturday that its request to visit had “not been granted” and did not immediately respond to the Russian statement.
The Kremlin has maintained that Ukraine attacked the prison to deter defectors, while the Ukrainian authorities rejected the narrative as absurd. They said that the deaths were a premeditated atrocity committed by Russian forces from within the prison, where survivors have described deplorable conditions and ritual abuses.
Mykhailo Podoliak, an adviser to Ukraine’s president, told The New York Times on Saturday that expert analysis of photos and videos released by Russia indicated that the center of the explosion was inside the building, with the building’s exterior practically undamaged.
“Any military expert will say the consequences of the explosion are not similar to a missile or artillery strike,” he said.
On Sunday, he pointed to the satellite photos as further evidence.
“Satellite images show that only one building was damaged,” he said in a statement. “Photo analysis show a thermobaric explosion from the inside.”
Mr. Podoliak said that Ukrainian prisoners had been moved to the barracks where the explosion occurred only days before the incident and that it was suspicious that no Russian soldiers or workers at the prison were injured.
He accused Russia of moving debris from other locations where the Ukrainians have hit targets using American-made precision missiles to the prison camp before the explosion.
“This, as well as the speed and organization of Russian propaganda, indicates that the terrorist attack was planned,” he said in an interview. “The purpose of this despicable terrorist attack was to cover up the previously committed Russian war crimes against prisoners, discredit the armed forces of Ukraine, disrupt the supply of Western weapons and create tension in Ukrainian society.”
Tetiana Katrychenko, a Ukrainian rights activist whose organization has been in contact with prisoners in the camp, said one Ukrainian prisoner had called his wife on Thursday night and reported hearing an explosion around 11 p.m.
“Not shelling, but just an explosion,” Ms. Katrychenko said, adding that she had a recording of the call. “He also said that two of his friends were taken out of the prison, where he is, earlier on the same day when the explosion happened.”
One of his friends was injured in the blast and another was killed, she said. Soldiers held in other parts of the camp have relayed similar accounts to their own family members, Ms. Katrychenko said.