Ukrainian forces struck an industrial site deep inside Russia on Saturday, which Ukraine and unofficial Russian news channels say was a key state-owned missile factory.

Our model suggests that Russian casualties are now between 1.1m and 1.4m, of whom 230,000-430,000 are dead. That would mean one in 25 Russian men between the ages of 18 and 49 may have been killed or severely wounded since the start of the full-scale war.

The staggering figure from four years of fighting is larger than the population of an Australian capital city.

Vladimir Putin has been honouring members of Russia's military in Moscow - amid speculation around unexpected divides emerging in the country's elite. Elsewhere, Ukraine's security service says drones have hit the Kaleykino oil refinery in Russia's Tatarstan region.

Serhii Kyslytsia is among those trying to negotiate an end to the conflict, which is entering its fifth year.

Elite Ukrainian troops have recaptured more than 400 square kilometers of territory along a chunk of the southern front lines since late January, Oleksandr Syrskyi, the commander-in-chief of Ukraine's military, said in a post to messaging app Telegram on Monday.

Experts say Vladimir Putin has peruaded U.S. negotiators that he wants to cut a deal – even as Moscow rains missiles and drones on Ukrainian cities.

Emergency crews have restored power to most areas hit by cuts after a major Ukrainian attack on energy infrastructure, the Russia-installed governor of the part of Zaporizhzhia region controlled by Moscow said.