Ukrainian prosecutors work to document evidence of war crimes in Kharkiv.

KYIV, Ukraine — Ukrainian prosecutors working in the northeast of the country to document evidence of war crimes and other atrocities face a monumental task in coming weeks as they treat hundreds of villages and towns spread across thousands of square miles as a crime scene.

They have compared the unfolding situation to some of the worst atrocities already documented in places like Bucha, a town a few miles west of Kyiv, but played out over months instead of days and stretching over an area half the size of Connecticut.

“We have a terrible picture of what the occupiers did, in particular, in the Kharkiv region,” Andriy Kostin, Ukraine’s prosecutor general, said in a statement this week. “In fact, now such cities as Balaklia, Izium are standing in the same row as Bucha, Borodianka, Irpin.”

Before the Russians were routed and driven out last weekend, they controlled roughly 34 percent of the Kharkiv region, he said.

The New York Times documented the torture, rape and execution of civilians by Russian soldiers in Bucha and other cities around Ukraine after Russian forces were forced to withdraw in the spring. But the situations are not identical.

In Bucha, for instance, bodies littered the streets and Russia’s hasty withdrawal gave its forces little time to cover up killings of civilians. In Kharkiv, Ukrainians fear, they have had months to cover up any crimes.

Russia has denied targeting civilians and made the baseless assertion that evidence of war crimes in places like Bucha was staged.

Ukraine has dispatched 23 mobile investigative and prosecutorial groups to work across Kharkiv. The teams include employees of the prosecutor’s office, the intelligence services, the National Police and explosives experts.

“They will conduct inspections of destroyed objects of civil infrastructure and deal with facts of murders of local residents,” Mr. Kostin said.

Five investigative groups will be dedicated to “deal exclusively with the facts of torture of local residents, as well as the search for the location of headquarters or command posts of the Russian military in the liberated territories,” Mr. Kostin added.

Yuriy Belousov, Ukraine’s chief war crimes prosecutor, said that in the past there were problems of coordination between national and local authorities.

“For example, several investigations by different law enforcement agencies were carried out simultaneously on the same fact,” he said. “There were cases of not very effective coordination between investigators and prosecutors, when they did not exchange information, which harmed the investigation.”

Now, he said, when a criminal case is registered a single team works throughout this community collecting all available evidence. “No one else goes there,” he said.