KYIV, Sept 15 - Ukrainian authorities found a mass burial site near a recaptured northeastern city previously occupied by Russian forces, President Volodymyr Zelensky announced Thursday night.

The grave was discovered close to Izium in the Kharkiv region, The Associated Press reported.

“The necessary procedures have already begun there. More information — clear, verifiable information — should be available tomorrow,” Zelensky said in his nightly televised address.

Hundreds of graves with simple wooden crosses were found in the trees in a forest outside Izium, most of them marked only with numbers. A larger grave bore a marker saying it contained the bodies of 17 Ukrainian soldiers.

Investigators with metal detectors were scanning the site for any hidden explosives.

Oleg Kotenko, an official with the Ukrainian ministry tasked with reintegrating occupied territories, said videos that Russian soldiers posted on social media indicated there were likely more than 17 bodies in the grave.

“We haven’t counted them yet, but I think there are more than 25 or even 30,” he said.

Izium resident Sergei Gorodko said that among the hundreds buried in individual graves were dozens of adults and children killed in a Russian airstrike on an apartment building.

He said he pulled some of them out of the rubble “with my own hands.”

Zelensky invoked the names of other Ukrainian cities where authorities said retreating Russian troops left behind mass graves of civilians and evidence of possible war crimes.

“Bucha, Mariupol, now, unfortunately, Izium. … Russia leaves death everywhere. And it must be held accountable for it. The world must bring Russia to real responsibility for this war,” he said in the address.

Sergei Bolvinov, a senior investigator for Ukrainian police in the eastern Kharkiv region, told British TV broadcaster Sky News that a pit containing more than 440 bodies was discovered near Izium after Kyiv’s forces swept in. He described the grave as “one of the largest burial sites in any one liberated city.”

Some of the people buried in the pit were shot. Others died from artillery fire, mines or airstrikes. Many of the bodies have not been identified yet, Bolvinov said.

Russian forces left Izium and other parts of the Kharkiv region last week amid a stunning Ukrainian counteroffensive. On Wednesday, Zelensky made a rare trip outside the capital to watch the national flag being raised over Izium’s city hall.

Deputy Interior Minister Yevhen Enin said Thursday night that other evidence found after Kyiv’s sweeping advance into the Kharkiv region included multiple “torture chambers” where both Ukrainian citizens and foreigners were detained “in completely inhuman conditions.”

“We have already come across the exhumation of individual bodies, not only with traces of a violent death, but also of torture — cut off ears, etc. This is just the beginning,” Enin told Ukraine’s Radio NV. (ap/ez)