Explosion Kills Ukrainian POWs Held by Russian-Backed Forces

Ukraine’s General Staff accused Russia of striking the facility in Olenivka, a town in the Donetsk region controlled by Russian forces, and killing Ukrainian prisoners it had taken, “to hide the torture of prisoners and executions committed there.” The General Staff said that Ukraine’s armed forces hadn’t launched any rocket or artillery strikes in the Olenivka area that night and that they use high-precision Western weapons such as Himars only against Russian military targets.

Ukrainian military intelligence later Friday accused Russian mercenary company Wagner Group of striking the facility under the personal direction of Yevgeny Prigozhin and said the strike wasn’t coordinated with the Russian Defense Ministry. According to Western officials, Wagner is financed by Mr. Prigozhin, a wealthy businessman close to the Kremlin, and its soldiers are involved in Russia’s offensive in Ukraine. Mr. Prigozhin’s representatives didn’t immediately respond to a request for comment.

Russian Defense Ministry spokesman Maj. Gen. Igor Konashenkov said the explosion at the detention facility was caused by Ukraine using U.S.-provided Himars rocket launchers, weapons that have inflicted major damage on Russian forces in recent weeks. He accused Ukraine of deliberately targeting its own captured soldiers to deter others from surrendering.

Russian-installed authorities in eastern Ukraine said 50 Ukrainian prisoners had died out of 193 people who were being held in a separate barracks at the detention center and were mainly members of the Azov battalion, which held out against overwhelming Russian forces for weeks during the siege of the strategic port city of Mariupol this spring. They said no guards were injured in the strike.

The battalion’s former commander accused Russia of staging the attack on the detention camp. “The Russian command framed the mass killing of prisoners as the actions of the Ukrainian army,” Andriy Biletsky wrote on social media. “It is already obvious that this was a preplanned act.”

The International Committee of the Red Cross registered Ukrainian prisoners of war from the Azovstal plant in Mariupol to guarantee their humane treatment in accordance with the Geneva Conventions. The ICRC didn’t immediately respond to a request for comment.

“It was a deliberate Russian war crime, a deliberate mass murder of Ukrainian prisoners of war,” Ukrainian President Volodymyr Zelensky said in his nightly address Friday. He called on the ICRC and the United Nations to protect Ukrainian prisoners of war. He added, “there should be a clear legal recognition of Russia as a state sponsor of terrorism. I am especially appealing to the United States of America—a solution is needed, needed now.”

Ukrainian officials also reacted with outrage after an unverified video that appeared to show the castration of a Ukrainian prisoner of war by a Russian soldier circulated on social media.

The video, which was circulated by pro-Kremlin bloggers embedded with Russian forces, among others, couldn’t be independently authenticated. The furor over the video comes as Ukrainian authorities are trying to gather evidence to prosecute Russian forces for alleged war crimes, including alleged atrocities committed against civilians in Bucha, Irpin, Mariupol and other Ukrainian cities and towns.

The video shows a man with the “Z” marking borne by Russian forces on his uniform castrating a prisoner in military fatigues.

Ukrainian presidential adviser Mykhailo Podolyak accused Russian propagandists of “delightedly” showing how Russian soldiers had mutilated a Ukrainian captive. “The fog of war will not help to avoid punishment for the executioners. We will identify and get to each of you,” Mr. Podolyak wrote on Twitter on Friday.

There was no immediate comment from Russian officials about the video. Kremlin spokesman Dmitry Peskov has previously dismissed allegations that Russian forces had committed war crimes, saying, “It is unacceptable to throw around such terms, especially against the backdrop of a large number of fakes.”

Five people were killed and at least a dozen injured Friday morning in the southern city of Mykolaiv, after Russian forces fired cluster munitions at a crowded intersection, Mayor Oleksandr Senkevych said.

“These were ordinary people who were going about their affairs,” he told reporters, saying some people died while crossing the street, others while waiting for their bus. “I hope the people who press these buttons see the grief they are bringing.”

Writing on his Telegram channel early Friday, Mr. Zelensky noted Thursday’s Russian missile strikes on the Kyiv region, Kropyvnytskyi and Mykolaiv and what he called “a series of strategically senseless and brutal onslaughts on Donbas.”

“I thank each and every one who repels this terror,” Mr. Zelensky wrote.

The U.S. Senate on Thursday passed a resolution calling on the State Department to designate Russia as a state sponsor of terrorism. Mr. Zelensky hailed the resolution, saying that “no one in the world is investing more in terrorism than Russia.”

Mr. Zelensky on Friday visited the port of Chornomorsk in the Odessa region on Ukraine’s Black Sea coast in advance of the expected renewal of grain shipments under a deal arranged with Turkey, Russia and the United Nations.

“We are ready to export Ukrainian grain,” he wrote on social media. “We are waiting for signals from our partners about the start of transportation. It is important for us to remain the guarantor of global food security.”

In a statement released by his office, Mr. Zelensky said a Turkish ship was being loaded with grain. “The port has started working,” he said.

Since its February invasion, Russia has blockaded Ukraine’s ports on the Black and Azov Seas, strangling the Ukrainian economy and imperiling essential grain exports to Asia and the Middle East. Some stores of grain housed at Ukrainian ports have spoiled, and the shipment of new harvests remains under threat.

Ukraine has tried to stop other countries from receiving grain stolen by Russia from occupied parts of the country. The Ukrainian ambassador to Lebanon spoke on Thursday with Lebanese President Michel Aoun about the arrival of a cargo ship laden with barley allegedly taken from Russian-occupied territories.

“A request was made to take measures to clarify the circumstances of its stay in Lebanese territorial waters,” the Ukrainian Embassy in Lebanon wrote on its Facebook page. “It was also emphasized that this fact can harm bilateral relations.”

Ukraine’s General Staff said Friday that Russian forces had launched fresh attacks in the Chernihiv and Sumy regions in the country’s north, as well in the Kharkiv region along the Russian border, using attack helicopters and artillery.

Kharkiv Mayor Ihor Terekhov wrote on Telegram that Russia had struck the city center twice early Friday, hitting a school. He said workers from the emergency services were sorting through the rubble. “So far, there are no reports of casualties or deaths,” he said. “I hope there won’t be.”

The Institute for the Study of War, a Washington-based think tank, said that Russia had made no territorial gains in and around Kharkiv but that Moscow might be setting conditions for renewed offensive operations in the area.

The ISW said Russia has attempted limited ground assaults and is likely suffering territorial losses in the Kherson region of southern Ukraine, where Ukrainian forces are seeking to retake land captured by Russia early in its invasion.

Ukrainian insurgents in Russian-occupied Kherson have conducted a series of attacks on Russian-installed officials in recent weeks, including targeting a police vehicle and injuring two officers this week with an improvised explosive device. On Friday, Russian-installed police said they had detained a resident who possessed a “cache of weapons and ammunition.”

Ukraine’s General Staff said that Russia’s significant combat losses had resulted in a shortage of officers. To plug these holes, the general staff said on social media, Moscow has resorted to the “mass assignment of the officer rank of ‘junior lieutenant’ to noncommissioned officers without relevant experience.”

In Russia, President Vladimir Putin met with the deputy prime minister for construction and regional development, Marat Khusnullin, and instructed him to lead reconstruction efforts in the mostly Russian-occupied eastern Ukrainian regions of Donetsk and Luhansk. While Ukraine still holds about a third of the Donetsk region, Russia claimed to have captured all of the Luhansk region earlier this month.

Mr. Khusnullin said that it would take three years to repair Mariupol in the Donetsk region, which lies in ruin after weeks of Russian bombardment that destroyed most of its infrastructure and housing.

Russian Foreign Minister Sergei Lavrov spoke with U.S. Secretary of State Antony Blinken on Friday for the first time since the February invasion. Mr. Lavrov told Mr. Blinken that weapons sent to Ukraine by the U.S. and North Atlantic Treaty Organization are preserving the agony of the regime in Kyiv, according to a statement from Russia’s Foreign Ministry. He suggested quiet diplomacy as a way of resolving the issue of Americans detained in Russia through a potential prisoner swap, according to the statement.

Mr. Blinken told reporters in Washington that he sought to dissuade Russia from annexing more Ukrainian territory and urged Russia to accept a U.S. offer to free women’s basketball star Brittney Griner and a former U.S. Marine convicted of espionage, Paul Whelan. He declined to say how Mr. Lavrov responded.

—Yaroslav Trofimov in Mykolaiv, Ukraine, contributed to this article.

Write to Brett Forrest at brett.forrest@wsj.com and Evan Gershkovich at evan.gershkovich@wsj.com