The head of the Russian parliament further fuelled mistrust as he spoke out against a prisoner exchange following the capture of Ukrainian fighters in Mariupol.
"Nazi criminals are not subject to exchange. They are war criminals and we must do everything to bring them to justice," Vyacheslav Volodin said during a plenary session.
Ukraine hopes for an exchange of the more than 260 of its own soldiers who had left the besieged Azovstal steelworks.
Some of the Ukrainian fighters in Mariupol belong to the far-right nationalist Azov regiment, seen by Moscow as a neo-Nazi unit.
The Russian military said it had captured 265 Ukrainian fighters from the plant since Monday.
"In the past 24 hours, 265 fighters, including 51 seriously wounded, have laid down their weapons and were taken into captivity," Russian Defence Ministry spokesman Igor Konashenkov said.
The numbers differ slightly from Kiev's information, which spoke of 264 prisoners, among them 52 seriously injured.
The Russian ministry published a video showing the capture of the Ukrainians, medical treatment being administered and the injured being taken away.
Efforts to rescue the last remaining Ukrainian soldiers in Mariupol continue, according to Kiev.
"We are working on further stages of the humanitarian operation," Ukrainian Deputy Prime Minister Iryna Vereshchuk wrote on Telegram.
Hundreds of civilians were evacuated from the plant in recent days.
Meanwhile, British intelligence said Russian armed forces are increasingly relying on "indiscriminate artillery bombardment" of Ukraine and "an unwillingness to risk flying combat aircraft routinely beyond its own front lines."
Several buildings were attacked in the western Russian region of Kursk on the border with Ukraine, Kursk Governor Roman Starovoyt announced. This could not be independently verified.
Seven civilians were killed in Ukraine's eastern Donetsk region by Russian troops, the head of the local military administration said.
At least 382 civilians have been killed and 1,096 injured in Donetsk alone since Russia's invasion, according to Ukrainian figures.
Russia's Deputy Prime Minister Marat Khusnullin visited Ukraine's Kherson on Tuesday, and said the region would take a "worthy place in our Russian family," RIA Novosti reported.
His visit came days after the Russian-installed government in the Ukrainian province said it plans to appeal to Moscow for the right to become part of Russia.
The developments in the war came as Sweden and Finland were on the verge of joining the western defence alliance NATO and the International Criminal Court (ICC) sent a team of 42 experts to Ukraine to investigate possible war crimes.
