Lyudmyla Denisova, Ukraine's ombudswoman, said 402,000 people, including 84,000 children, have been taken against their will.
The Kremlin gave nearly identical numbers for those who have been relocated, but said they wanted to go to Russia.
Ukraine's rebel-controlled eastern regions are predominantly Russian-speaking, and many people there have supported close ties to Moscow.
Russian Colonel General Mikhail Mizintsev said the roughly 400,000 people evacuated to Russia since the start of the military action were from the Donetsk and Luhansk regions in eastern Ukraine, where pro-Moscow separatists have been fighting for control for nearly eight years.
Russian authorities said they are providing accommodation and dispensing payments to the evacuees.
But Donetsk Region Governor Pavlo Kyrylenko said, "People are being forcibly moved into the territory of the aggressor state".
Denisova said those removed included a 92-year-old woman in Mariupol who was forced to go to Taganrog in southern Russia.
Ukrainian officials said the Russians are taking people's passports and moving them to "filtration camps" in Ukraine's separatist-controlled east before sending them to various distant, economically depressed areas in Russia.
Among those taken, Ukraine's Foreign Ministry charged, were 6000 residents of Mariupol, the devastated port city in the country's east.
Moscow's troops are confiscating identity documents from an additional 15,000 people in a section of Mariupol under Russian control, the ministry said.
Some could be sent as far as the Pacific island of Sakhalin, Ukrainian intelligence said, and are being offered jobs on condition they do not leave for two years.
The ministry said the Russians intend to "use them as hostages and put more political pressure on Ukraine."
Kyrylenko said Mariupol's residents had been long deprived of information and that the Russians feed them false claims about Ukraine's defeats to persuade them to move to Russia.
"Russian lies may influence those who have been under the siege," he said.