Russia will not suspend its military operation in Ukraine during potential talks on the situation, the Interfax news agency reports the Kremlin to say.

Earlier, Ukrainian President Volodymyr Zelenskyy agreed to talks with Russia at the Belarusian-Ukrainian border.

Zelensky said he held substantive talks with his Belarusian counterpart Alexander Lukashenko, who offered to host the talks.

According to the United Nations, 64 civilians have died and 174 have been injured since Russian troops crossed the border.

Four days since entering Ukraine, Russian troops entered Kharkiv, the country's second city, and engaged in gunfights.

Russian President Vladimir Putin on Sunday ordered Russia's deterrence forces - a reference to units which include nuclear arms - on high alert in response to measures taken against his military operation in Ukraine.

(With input from agencies)