Ukrainian authorities have found a mass burial site containing more than 440 bodies in a forest just outside the eastern city of Izium, which was recently recaptured from Russian forces, a regional police official says.
Serhiy Bolvinov, the chief police investigator for Kharkiv region, told Sky News that forensic investigations would be carried out on every body, some of which had been killed by shelling and air strikes.
"I can say it is one of the largest burial sites in a big town in liberated [areas]... 440 bodies were buried in one place," Mr Bolvinov said.
President Volodymyr Zelenskyy put the blame on Russia and likened the discovery to what happened in Bucha, on the outskirts of the capital Kyiv, in the early stages of the late February invasion by Russian forces.
Ukraine and its Western allies have accused Russian forces of perpetrating war crimes there.
"More information — clear, verified information — should be available tomorrow," Mr Zelenskyy said in a video address to the nation, adding that journalists from around the world would be taken to the site on Friday.
"We want the world to know what is really happening and what the Russian occupation has led to," he said.
Associated Press journalists saw the site in a forest outside Izium on Thursday.
A mass grave bore a marker saying it contained the bodies of 17 Ukrainian soldiers. It was surrounded by hundreds of individual graves with only crosses to mark them.
Ukrainian investigators were at work examining the site with metal detectors 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 marked mass 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 the individual graves were dozens of adults and children killed in a Russian air strike on an apartment building.
He said he pulled some of them out of the rubble "with my own hands."
Russian troops retreated from Izium and other parts of the Kharkiv region last week amid a stunning Ukrainian counteroffensive.
On Wednesday, Mr Zelenskyy made a rare trip outside Ukraine's capital to watch the raising of the national flag at Izium's city hall.
Later he 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."
'This is just the beginning'
Ukraine's deputy interior minister said 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, [for example]. This is just the beginning," Yevhen 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.
Mr Enin did not specify where the students were held, although he named the small cities of Balakliya and Volchansk as two locations where the alleged torture chambers were found.
His account could not be independently verified.
"All these traces of war crimes are now carefully documented by us," he said.
"And we know from the experience of Bucha that the worst crimes can only be exposed over time."
That was a reference to a Kyiv suburb where the bodies of hundreds of civilians were discovered following the Russian army's withdrawal from the area in March.
Ukrainian advance set to slow
After a week of rapid Ukrainian gains in the north-east, Ukrainian officials said Russian forces were fortifying their defences and it would be hard to maintain the pace of the advance.
Russian President Vladimir Putin has yet to comment publicly on the setback suffered by his forces this month, in which Ukraine says it retook about 9,000 square kilometres of territory.
The speed of the advance has bolstered Ukrainian morale, and given it some success to show its Western allies as it seeks more weapons to sustain its defence.
In Washington, US President Joe Biden announced a new $US600 million ($895 million) arms package to help Ukraine, including High Mobility Artillery Rocket Systems (HIMARS) and artillery rounds.
Meanwhile, Russian forces shelled Kharkiv city and other towns in the region on Thursday, Ukrainian officials said, as well as a region on the border with Russia.
On the Russian side, Vyacheslav Gladkov, the governor of Russia's Belgorod region, said the Ukrainian army shelled the town of Valuyki near the border.
"Anti-aircraft defences went into action but there is some destruction on the ground," he said on Telegram, referring to a power substation put out of commission and private homes and vehicles set on fire.
Reuters was not able to verify battlefield reports.
China's concerns about conflict
Mr Putin said on Thursday he understood China's leader Xi Jinping had concerns about the crisis in Ukraine, a surprise acknowledgement of friction with Beijing over the war.
Since Russia invaded Ukraine, China has trod a careful line, criticising Western sanctions against Moscow but stopping short of endorsing or assisting in the military campaign.
"We understand your questions and concern about this. During today's meeting, we will of course explain our position," Mr Putin told Mr Xi in Uzbekistan at their first meeting since the war began.
Mr Xi did not mention Ukraine in his public remarks, nor was it mentioned in a Chinese account of the meeting.
Russian Foreign Minister Sergei Lavrov later told reporters the talks with China has been excellent.
The last time Mr Putin and Mr Xi met, they signed a "no limits" friendship agreement between their countries.
Three weeks later, Russia invaded Ukraine in what it called a "special military operation" to "disarm" its smaller neighbour.
Ukraine and the West have accused Russia of waging an unprovoked war of aggression.
ABC/wires
