Ukrainian President Volodymyr Zelensky has warned that the worst atrocities committed by Russian troops departing from the north of the country are yet to be discovered.
He said the town of Borodyanka may have suffered more than others.
Horrific images of bodies in streets in towns like Bucha have generated shock and condemnation worldwide.
Ukrainian intelligence officials said Russian units based in the region would be sent back to eastern Ukraine.
The 64th motorised rifle brigade – which they allege committed atrocities in Bucha – would return to the conflict within weeks, probably to the Kharkiv area, they said.
Russia denies killing civilians, and without evidence says Ukraine staged the scenes.
he Ukrainian government started a war crimes investigation after it said the bodies of 410 civilians had been found in areas around Kyiv.
Some were discovered in mass graves while others had their hands tied and had apparently been shot at close range.
Officials in Kyiv also accused Russian forces of killing a village head, her husband and her son in the village of Motyzhyn for aiding Ukrainian troops in the area.
There are also reports of at least three apparently tortured bodies in the town of Konotop in another northern region, Sumy.
The images from Bucha prompted US President Joe Biden to call for his Russian counterpart Vladimir Putin to be tried for war crimes.
His intervention came as new satellite photos by the earth observation company Maxar showing bodies lining Bucha’s streets during its occupation by Russian forces were published.
‘Worse than IS’
Foreign Minister Dmytro Kuleba told a news conference in Warsaw on Monday that the killings were the “tip of the iceberg” and demanded more severe sanctions against Russia.
In a BBC interview, he cited the desperate situation in the southern town of Mariupol, which has been under Russian bombardment for weeks.
“What we’ve seen in recent weeks is that Russia is much worse than Isis [the Islamic State group] when it comes to its atrocities and massacres,” he said.
In his nightly address to the Ukrainian people, Mr Zelensky said things were done throughout the region north of Kyiv that people had not seen since the Nazi occupation.
“There is already information that the number of victims may be even higher in Borodyanka and some other liberated cities,” he said.
Mr Zelensky is due to speak to the United Nations Security Council later on Tuesday, where he is expected to offer more evidence of atrocities.
War in Ukraine: More coverage
Several Western nations have expelled Russian diplomats in response to the discovery of the atrocities, and new sanctions against Russia are being discussed.
Italy announced on Tuesday it was expelling 30 Russian officials, Denmark 15 and Sweden three. Germany and France announced similar measures on Monday, and Lithuania expelled the Russian ambassador. Russia has vowed to retaliate.
European Commission President Ursula von der Leyen and foreign affairs chief Josep Borrell will travel to Kyiv to meet the Ukrainian president later in the week, Ms von der Leyen’s spokesman said.
But Moscow’s ambassador to the UN said Russia would present “empirical evidence” to the UN Security Council demonstrating that Western statements on events at Bucha were lies.
Defence Ministry spokesman Igor Konashenkov said that in the village of Moshchun northwest of Kyiv Ukrainian psychological operations troops had filmed fake footage of dead civilians.