KIEV — Ukrainian authorities have started unearthing bodies they found at a mass burial site near Izium, a city in the country's northeast that was occupied by Russian forces and recently retaken by Ukraine as part of a lightning-fast counteroffensive.

Regional governor Oleg Synehubov said on Friday evening that 99% of the bodies exhumed Friday in the eastern Ukrainian city of Izum "showed signs of violent death".

The head of the prosecutor's office in the Kharkiv region said some of the bodies found showed signs of torture. Certain corpses were found with their hands tied behind their back or with ropes around their neck, according to them.

More than 1,000 Ukrainian citizens are believed to have been tortured and killed in the liberated territories in the Kharkiv region, a domestic human rights official added on Friday.

Ukrainian President Volodymyr Zelensky previously said that what had been found was an example of "what the Russian occupation has led to".

While speaking to Reuters on Friday, he also accused Moscow of torture and war crimes in Ukraine's northeast and likened the aftermath in the recaptured areas to Russia's withdrawal from near Kiev months ago.

"As of today, there are 450 dead people, buried. But there are others, separate burials of many people. Tortured people. Entire families in certain territories," the Ukrainian leader said.

AP journalists saw the site Thursday in a forest outside of the town of almost 50,000, witnessing hundreds of graves with simple wooden crosses amid the trees, 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 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 Kiev’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 Kiev’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 said in an interview with Ukraine’s Radio NV.

He claimed that among those held at one of the sites were students from an unspecified Asian country who were captured at a Russian checkpoint as they tried to leave for Ukrainian-controlled territory.

Enin did not specify where the students were held, although he named the small cities of Balakliya and Volchansk as two locations where torture chambers were found. His account could not be independently verified.

“All these traces of war crimes are now carefully documented by us. And we know from the experience of Bucha that the worst crimes can only be exposed over time,” Enin said, in a reference to a Kiev suburb where the bodies of hundreds of civilians were discovered following the Russian army’s withdrawal from the area in March.

Earlier on Thursday, Zelensky said that during the five months the Russians occupied the region, they “only destroyed, only deprived, only took away".

"They left behind devastated villages; in some of them there is not a single undamaged house. The occupiers turned schools into garbage dumps and churches — shattered, literally turned into toilets.” — Euronews